module Enumerable

What’s Here

Module Enumerable provides methods that are useful to a collection class for:

Methods for Querying

These methods return information about the Enumerable other than the elements themselves:

include?, member?

Returns true if self == object, false otherwise.

all?

Returns true if all elements meet a specified criterion; false otherwise.

any?

Returns true if any element meets a specified criterion; false otherwise.

none?

Returns true if no element meets a specified criterion; false otherwise.

one?

Returns true if exactly one element meets a specified criterion; false otherwise.

count

Returns the count of elements, based on an argument or block criterion, if given.

tally

Returns a new Hash containing the counts of occurrences of each element.

Methods for Fetching

These methods return entries from the Enumerable, without modifying it:

Leading, trailing, or all elements:

entries, to_a

Returns all elements.

first

Returns the first element or leading elements.

take

Returns a specified number of leading elements.

drop

Returns a specified number of trailing elements.

take_while

Returns leading elements as specified by the given block.

drop_while

Returns trailing elements as specified by the given block.

Minimum and maximum value elements:

min

Returns the elements whose values are smallest among the elements, as determined by <=> or a given block.

max

Returns the elements whose values are largest among the elements, as determined by <=> or a given block.

minmax

Returns a 2-element Array containing the smallest and largest elements.

min_by

Returns the smallest element, as determined by the given block.

max_by

Returns the largest element, as determined by the given block.

minmax_by

Returns the smallest and largest elements, as determined by the given block.

Groups, slices, and partitions:

group_by

Returns a Hash that partitions the elements into groups.

partition

Returns elements partitioned into two new Arrays, as determined by the given block.

slice_after

Returns a new Enumerator whose entries are a partition of self, based either on a given object or a given block.

slice_before

Returns a new Enumerator whose entries are a partition of self, based either on a given object or a given block.

slice_when

Returns a new Enumerator whose entries are a partition of self based on the given block.

chunk

Returns elements organized into chunks as specified by the given block.

chunk_while

Returns elements organized into chunks as specified by the given block.

Methods for Searching and Filtering

These methods return elements that meet a specified criterion.

find, detect

Returns an element selected by the block.

find_all, filter, select

Returns elements selected by the block.

find_index

Returns the index of an element selected by a given object or block.

reject

Returns elements not rejected by the block.

uniq

Returns elements that are not duplicates.

Methods for Sorting

These methods return elements in sorted order.

sort

Returns the elements, sorted by <=> or the given block.

sort_by

Returns the elements, sorted by the given block.

Methods for Iterating

each_entry

Calls the block with each successive element (slightly different from each).

each_with_index

Calls the block with each successive element and its index.

each_with_object

Calls the block with each successive element and a given object.

each_slice

Calls the block with successive non-overlapping slices.

each_cons

Calls the block with successive overlapping slices. (different from each_slice).

reverse_each

Calls the block with each successive element, in reverse order.

Other Methods

map, collect

Returns objects returned by the block.

filter_map

Returns truthy objects returned by the block.

flat_map, collect_concat

Returns flattened objects returned by the block.

grep

Returns elements selected by a given object or objects returned by a given block.

grep_v

Returns elements selected by a given object or objects returned by a given block.

reduce, inject

Returns the object formed by combining all elements.

sum

Returns the sum of the elements, using method +++.

zip

Combines each element with elements from other enumerables; returns the n-tuples or calls the block with each.

cycle

Calls the block with each element, cycling repeatedly.

Usage

To use module Enumerable in a collection class:

Example:

class Foo
  include Enumerable
  def each
    yield 1
    yield 1, 2
    yield
  end
end
Foo.new.each_entry{ |element| p element }

Output:

1
[1, 2]
nil

Enumerable in Ruby Core Classes

Some Ruby classes include Enumerable:

Virtually all methods in Enumerable call method #each in the including class:

About the Examples

The example code snippets for the Enumerable methods:

Public Instance Methods

all? → true or false click to toggle source
all?(pattern) → true or false
all? {|element| ... } → true or false

Returns whether every element meets a given criterion.

With no argument and no block, returns whether every element is truthy:

(1..4).all?           # => true
%w[a b c d].all?      # => true
[1, 2, nil].all?      # => false
['a','b', false].all? # => false
[].all?               # => true

With argument pattern and no block, returns whether for each element element, pattern === element:

(1..4).all?(Integer)                 # => true
(1..4).all?(Numeric)                 # => true
(1..4).all?(Float)                   # => false
%w[bar baz bat bam].all?(/ba/)       # => true
%w[bar baz bat bam].all?(/bar/)      # => false
%w[bar baz bat bam].all?('ba')       # => false
{foo: 0, bar: 1, baz: 2}.all?(Array) # => true
{foo: 0, bar: 1, baz: 2}.all?(Hash)  # => false
[].all?(Integer)                     # => true

With a block given, returns whether the block returns a truthy value for every element:

(1..4).all? {|element| element < 5 }                    # => true
(1..4).all? {|element| element < 4 }                    # => false
{foo: 0, bar: 1, baz: 2}.all? {|key, value| value < 3 } # => true
{foo: 0, bar: 1, baz: 2}.all? {|key, value| value < 2 } # => false

Related: any?, none? one?.

static VALUE
enum_all(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo = MEMO_ENUM_NEW(Qtrue);
    WARN_UNUSED_BLOCK(argc);
    rb_block_call(obj, id_each, 0, 0, ENUMFUNC(all), (VALUE)memo);
    return memo->v1;
}
any? → true or false click to toggle source
any?(pattern) → true or false
any? {|element| ... } → true or false

Returns whether any element meets a given criterion.

With no argument and no block, returns whether any element is truthy:

(1..4).any?          # => true
%w[a b c d].any?     # => true
[1, false, nil].any? # => true
[].any?              # => false

With argument pattern and no block, returns whether for any element element, pattern === element:

[nil, false, 0].any?(Integer)        # => true
[nil, false, 0].any?(Numeric)        # => true
[nil, false, 0].any?(Float)          # => false
%w[bar baz bat bam].any?(/m/)        # => true
%w[bar baz bat bam].any?(/foo/)      # => false
%w[bar baz bat bam].any?('ba')       # => false
{foo: 0, bar: 1, baz: 2}.any?(Array) # => true
{foo: 0, bar: 1, baz: 2}.any?(Hash)  # => false
[].any?(Integer)                     # => false

With a block given, returns whether the block returns a truthy value for any element:

(1..4).any? {|element| element < 2 }                    # => true
(1..4).any? {|element| element < 1 }                    # => false
{foo: 0, bar: 1, baz: 2}.any? {|key, value| value < 1 } # => true
{foo: 0, bar: 1, baz: 2}.any? {|key, value| value < 0 } # => false

Related: all?, none?, one?.

static VALUE
enum_any(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo = MEMO_ENUM_NEW(Qfalse);
    WARN_UNUSED_BLOCK(argc);
    rb_block_call(obj, id_each, 0, 0, ENUMFUNC(any), (VALUE)memo);
    return memo->v1;
}
chain(*enums) → enumerator click to toggle source

Returns an enumerator object generated from this enumerator and given enumerables.

e = (1..3).chain([4, 5])
e.to_a #=> [1, 2, 3, 4, 5]
static VALUE
enum_chain(int argc, VALUE *argv, VALUE obj)
{
    VALUE enums = rb_ary_new_from_values(1, &obj);
    rb_ary_cat(enums, argv, argc);
    return new_enum_chain(enums);
}
chunk {|array| ... } → enumerator click to toggle source

Each element in the returned enumerator is a 2-element array consisting of:

  • A value returned by the block.

  • An array (“chunk”) containing the element for which that value was returned, and all following elements for which the block returned the same value:

So that:

  • Each block return value that is different from its predecessor begins a new chunk.

  • Each block return value that is the same as its predecessor continues the same chunk.

Example:

e = (0..10).chunk {|i| (i / 3).floor } # => #<Enumerator: ...>
# The enumerator elements.
e.next # => [0, [0, 1, 2]]
e.next # => [1, [3, 4, 5]]
e.next # => [2, [6, 7, 8]]
e.next # => [3, [9, 10]]

Method chunk is especially useful for an enumerable that is already sorted. This example counts words for each initial letter in a large array of words:

# Get sorted words from a web page.
url = 'https://raw.githubusercontent.com/eneko/data-repository/master/data/words.txt'
words = URI::open(url).readlines
# Make chunks, one for each letter.
e = words.chunk {|word| word.upcase[0] } # => #<Enumerator: ...>
# Display 'A' through 'F'.
e.each {|c, words| p [c, words.length]; break if c == 'F' }

Output:

["A", 17096]
["B", 11070]
["C", 19901]
["D", 10896]
["E", 8736]
["F", 6860]

You can use the special symbol :_alone to force an element into its own separate chuck:

a = [0, 0, 1, 1]
e = a.chunk{|i| i.even? ? :_alone : true }
e.to_a # => [[:_alone, [0]], [:_alone, [0]], [true, [1, 1]]]

For example, you can put each line that contains a URL into its own chunk:

pattern = /http/
open(filename) { |f|
  f.chunk { |line| line =~ pattern ? :_alone : true }.each { |key, lines|
    pp lines
  }
}

You can use the special symbol :_separator or nil to force an element to be ignored (not included in any chunk):

a = [0, 0, -1, 1, 1]
e = a.chunk{|i| i < 0 ? :_separator : true }
e.to_a # => [[true, [0, 0]], [true, [1, 1]]]

Note that the separator does end the chunk:

a = [0, 0, -1, 1, -1, 1]
e = a.chunk{|i| i < 0 ? :_separator : true }
e.to_a # => [[true, [0, 0]], [true, [1]], [true, [1]]]

For example, the sequence of hyphens in svn log can be eliminated as follows:

sep = "-"*72 + "\n"
IO.popen("svn log README") { |f|
  f.chunk { |line|
    line != sep || nil
  }.each { |_, lines|
    pp lines
  }
}
#=> ["r20018 | knu | 2008-10-29 13:20:42 +0900 (Wed, 29 Oct 2008) | 2 lines\n",
#    "\n",
#    "* README, README.ja: Update the portability section.\n",
#    "\n"]
#   ["r16725 | knu | 2008-05-31 23:34:23 +0900 (Sat, 31 May 2008) | 2 lines\n",
#    "\n",
#    "* README, README.ja: Add a note about default C flags.\n",
#    "\n"]
#   ...

Paragraphs separated by empty lines can be parsed as follows:

File.foreach("README").chunk { |line|
  /\A\s*\z/ !~ line || nil
}.each { |_, lines|
  pp lines
}
static VALUE
enum_chunk(VALUE enumerable)
{
    VALUE enumerator;

    RETURN_SIZED_ENUMERATOR(enumerable, 0, 0, enum_size);

    enumerator = rb_obj_alloc(rb_cEnumerator);
    rb_ivar_set(enumerator, id_chunk_enumerable, enumerable);
    rb_ivar_set(enumerator, id_chunk_categorize, rb_block_proc());
    rb_block_call(enumerator, idInitialize, 0, 0, chunk_i, enumerator);
    return enumerator;
}
chunk_while {|element, next_element| ... } → enumerator click to toggle source

The returned Enumerator uses the block to partition elements into arrays (“chunks”); it calls the block with each element and its successor; begins a new chunk if and only if the block returns a truthy value:

Example:

a = [1, 2, 4, 9, 10, 11, 12, 15, 16, 19, 20, 21]
e = a.chunk_while {|i, j| j == i + 1 }
e.each {|array| p array }

Output:

[1, 2]
[4]
[9, 10, 11, 12]
[15, 16]
[19, 20, 21]
static VALUE
enum_chunk_while(VALUE enumerable)
{
    VALUE enumerator;
    VALUE pred;

    pred = rb_block_proc();

    enumerator = rb_obj_alloc(rb_cEnumerator);
    rb_ivar_set(enumerator, id_slicewhen_enum, enumerable);
    rb_ivar_set(enumerator, id_slicewhen_pred, pred);
    rb_ivar_set(enumerator, id_slicewhen_inverted, Qtrue);

    rb_block_call(enumerator, idInitialize, 0, 0, slicewhen_i, enumerator);
    return enumerator;
}
collect -> enumerator click to toggle source

Returns an array of objects returned by the block.

With a block given, calls the block with successive elements; returns an array of the objects returned by the block:

(0..4).map {|i| i*i }                               # => [0, 1, 4, 9, 16]
{foo: 0, bar: 1, baz: 2}.map {|key, value| value*2} # => [0, 2, 4]

With no block given, returns an Enumerator.

static VALUE
enum_collect(VALUE obj)
{
    VALUE ary;
    int min_argc, max_argc;

    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    ary = rb_ary_new();
    min_argc = rb_block_min_max_arity(&max_argc);
    rb_lambda_call(obj, id_each, 0, 0, collect_i, min_argc, max_argc, ary);

    return ary;
}
Also aliased as: map
collect_concat()

Returns an array of flattened objects returned by the block.

With a block given, calls the block with successive elements; returns a flattened array of objects returned by the block:

[0, 1, 2, 3].flat_map {|element| -element }                    # => [0, -1, -2, -3]
[0, 1, 2, 3].flat_map {|element| [element, -element] }         # => [0, 0, 1, -1, 2, -2, 3, -3]
[[0, 1], [2, 3]].flat_map {|e| e + [100] }                     # => [0, 1, 100, 2, 3, 100]
{foo: 0, bar: 1, baz: 2}.flat_map {|key, value| [key, value] } # => [:foo, 0, :bar, 1, :baz, 2]

With no block given, returns an Enumerator.

Alias: collect_concat.

Alias for: flat_map
compact → array click to toggle source

Returns an array of all non-nil elements:

a = [nil, 0, nil, 'a', false, nil, false, nil, 'a', nil, 0, nil]
a.compact # => [0, "a", false, false, "a", 0]
static VALUE
enum_compact(VALUE obj)
{
    VALUE ary;

    ary = rb_ary_new();
    rb_block_call(obj, id_each, 0, 0, compact_i, ary);

    return ary;
}
count → integer click to toggle source
count(object) → integer
count {|element| ... } → integer

Returns the count of elements, based on an argument or block criterion, if given.

With no argument and no block given, returns the number of elements:

[0, 1, 2].count                # => 3
{foo: 0, bar: 1, baz: 2}.count # => 3

With argument object given, returns the number of elements that are == to object:

[0, 1, 2, 1].count(1)           # => 2

With a block given, calls the block with each element and returns the number of elements for which the block returns a truthy value:

[0, 1, 2, 3].count {|element| element < 2}              # => 2
{foo: 0, bar: 1, baz: 2}.count {|key, value| value < 2} # => 2
static VALUE
enum_count(int argc, VALUE *argv, VALUE obj)
{
    VALUE item = Qnil;
    struct MEMO *memo;
    rb_block_call_func *func;

    if (argc == 0) {
        if (rb_block_given_p()) {
            func = count_iter_i;
        }
        else {
            func = count_all_i;
        }
    }
    else {
        rb_scan_args(argc, argv, "1", &item);
        if (rb_block_given_p()) {
            rb_warn("given block not used");
        }
        func = count_i;
    }

    memo = MEMO_NEW(item, 0, 0);
    rb_block_call(obj, id_each, 0, 0, func, (VALUE)memo);
    return imemo_count_value(memo);
}
cycle(n = nil) {|element| ...} → nil click to toggle source
cycle(n = nil) → enumerator

When called with positive integer argument n and a block, calls the block with each element, then does so again, until it has done so n times; returns nil:

a = []
(1..4).cycle(3) {|element| a.push(element) } # => nil
a # => [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4]
a = []
('a'..'d').cycle(2) {|element| a.push(element) }
a # => ["a", "b", "c", "d", "a", "b", "c", "d"]
a = []
{foo: 0, bar: 1, baz: 2}.cycle(2) {|element| a.push(element) }
a # => [[:foo, 0], [:bar, 1], [:baz, 2], [:foo, 0], [:bar, 1], [:baz, 2]]

If count is zero or negative, does not call the block.

When called with a block and n is nil, cycles forever.

When no block is given, returns an Enumerator.

static VALUE
enum_cycle(int argc, VALUE *argv, VALUE obj)
{
    VALUE ary;
    VALUE nv = Qnil;
    long n, i, len;

    rb_check_arity(argc, 0, 1);

    RETURN_SIZED_ENUMERATOR(obj, argc, argv, enum_cycle_size);
    if (!argc || NIL_P(nv = argv[0])) {
        n = -1;
    }
    else {
        n = NUM2LONG(nv);
        if (n <= 0) return Qnil;
    }
    ary = rb_ary_new();
    RBASIC_CLEAR_CLASS(ary);
    rb_block_call(obj, id_each, 0, 0, cycle_i, ary);
    len = RARRAY_LEN(ary);
    if (len == 0) return Qnil;
    while (n < 0 || 0 < --n) {
        for (i=0; i<len; i++) {
            enum_yield_array(RARRAY_AREF(ary, i));
        }
    }
    return Qnil;
}
detect(*args)

Returns the first element for which the block returns a truthy value.

With a block given, calls the block with successive elements of the collection; returns the first element for which the block returns a truthy value:

(0..9).find {|element| element > 2}                # => 3

If no such element is found, calls if_none_proc and returns its return value.

(0..9).find(proc {false}) {|element| element > 12} # => false
{foo: 0, bar: 1, baz: 2}.find {|key, value| key.start_with?('b') }            # => [:bar, 1]
{foo: 0, bar: 1, baz: 2}.find(proc {[]}) {|key, value| key.start_with?('c') } # => []

With no block given, returns an Enumerator.

Alias for: find
drop(n) → array click to toggle source

For positive integer n, returns an array containing all but the first n elements:

r = (1..4)
r.drop(3)  # => [4]
r.drop(2)  # => [3, 4]
r.drop(1)  # => [2, 3, 4]
r.drop(0)  # => [1, 2, 3, 4]
r.drop(50) # => []

h = {foo: 0, bar: 1, baz: 2, bat: 3}
h.drop(2) # => [[:baz, 2], [:bat, 3]]
static VALUE
enum_drop(VALUE obj, VALUE n)
{
    VALUE result;
    struct MEMO *memo;
    long len = NUM2LONG(n);

    if (len < 0) {
        rb_raise(rb_eArgError, "attempt to drop negative size");
    }

    result = rb_ary_new();
    memo = MEMO_NEW(result, 0, len);
    rb_block_call(obj, id_each, 0, 0, drop_i, (VALUE)memo);
    return result;
}
drop_while {|element| ... } → array click to toggle source
drop_while → enumerator

Calls the block with successive elements as long as the block returns a truthy value; returns an array of all elements after that point:

(1..4).drop_while{|i| i < 3 } # => [3, 4]
h = {foo: 0, bar: 1, baz: 2}
a = h.drop_while{|element| key, value = *element; value < 2 }
a # => [[:baz, 2]]

With no block given, returns an Enumerator.

static VALUE
enum_drop_while(VALUE obj)
{
    VALUE result;
    struct MEMO *memo;

    RETURN_ENUMERATOR(obj, 0, 0);
    result = rb_ary_new();
    memo = MEMO_NEW(result, 0, FALSE);
    rb_block_call(obj, id_each, 0, 0, drop_while_i, (VALUE)memo);
    return result;
}
each_cons(n) { ... } → self click to toggle source
each_cons(n) → enumerator

Calls the block with each successive overlapped n-tuple of elements; returns self:

a = []
(1..5).each_cons(3) {|element| a.push(element) }
a # => [[1, 2, 3], [2, 3, 4], [3, 4, 5]]

a = []
h = {foo: 0,  bar: 1, baz: 2, bam: 3}
h.each_cons(2) {|element| a.push(element) }
a # => [[[:foo, 0], [:bar, 1]], [[:bar, 1], [:baz, 2]], [[:baz, 2], [:bam, 3]]]

With no block given, returns an Enumerator.

static VALUE
enum_each_cons(VALUE obj, VALUE n)
{
    long size = NUM2LONG(n);
    struct MEMO *memo;
    int arity;

    if (size <= 0) rb_raise(rb_eArgError, "invalid size");
    RETURN_SIZED_ENUMERATOR(obj, 1, &n, enum_each_cons_size);
    arity = rb_block_arity();
    if (enum_size_over_p(obj, size)) return obj;
    memo = MEMO_NEW(rb_ary_new2(size), dont_recycle_block_arg(arity), size);
    rb_block_call(obj, id_each, 0, 0, each_cons_i, (VALUE)memo);

    return obj;
}
each_entry(*args) {|element| ... } → self click to toggle source
each_entry(*args) → enumerator

Calls the given block with each element, converting multiple values from yield to an array; returns self:

a = []
(1..4).each_entry {|element| a.push(element) } # => 1..4
a # => [1, 2, 3, 4]

a = []
h = {foo: 0, bar: 1, baz:2}
h.each_entry {|element| a.push(element) }
# => {:foo=>0, :bar=>1, :baz=>2}
a # => [[:foo, 0], [:bar, 1], [:baz, 2]]

class Foo
  include Enumerable
  def each
    yield 1
    yield 1, 2
    yield
  end
end
Foo.new.each_entry {|yielded| p yielded }

Output:

1
[1, 2]
nil

With no block given, returns an Enumerator.

static VALUE
enum_each_entry(int argc, VALUE *argv, VALUE obj)
{
    RETURN_SIZED_ENUMERATOR(obj, argc, argv, enum_size);
    rb_block_call(obj, id_each, argc, argv, each_val_i, 0);
    return obj;
}
each_slice(n) { ... } → self click to toggle source
each_slice(n) → enumerator

Calls the block with each successive disjoint n-tuple of elements; returns self:

a = []
(1..10).each_slice(3) {|tuple| a.push(tuple) }
a # => [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]]

a = []
h = {foo: 0, bar: 1, baz: 2, bat: 3, bam: 4}
h.each_slice(2) {|tuple| a.push(tuple) }
a # => [[[:foo, 0], [:bar, 1]], [[:baz, 2], [:bat, 3]], [[:bam, 4]]]

With no block given, returns an Enumerator.

static VALUE
enum_each_slice(VALUE obj, VALUE n)
{
    long size = NUM2LONG(n);
    VALUE ary;
    struct MEMO *memo;
    int arity;

    if (size <= 0) rb_raise(rb_eArgError, "invalid slice size");
    RETURN_SIZED_ENUMERATOR(obj, 1, &n, enum_each_slice_size);
    size = limit_by_enum_size(obj, size);
    ary = rb_ary_new2(size);
    arity = rb_block_arity();
    memo = MEMO_NEW(ary, dont_recycle_block_arg(arity), size);
    rb_block_call(obj, id_each, 0, 0, each_slice_i, (VALUE)memo);
    ary = memo->v1;
    if (RARRAY_LEN(ary) > 0) rb_yield(ary);

    return obj;
}
each_with_index(*args) {|element, i| ..... } → self click to toggle source
each_with_index(*args) → enumerator

With a block given, calls the block with each element and its index; returns self:

h = {}
(1..4).each_with_index {|element, i| h[element] = i } # => 1..4
h # => {1=>0, 2=>1, 3=>2, 4=>3}

h = {}
%w[a b c d].each_with_index {|element, i| h[element] = i }
# => ["a", "b", "c", "d"]
h # => {"a"=>0, "b"=>1, "c"=>2, "d"=>3}

a = []
h = {foo: 0, bar: 1, baz: 2}
h.each_with_index {|element, i| a.push([i, element]) }
# => {:foo=>0, :bar=>1, :baz=>2}
a # => [[0, [:foo, 0]], [1, [:bar, 1]], [2, [:baz, 2]]]

With no block given, returns an Enumerator.

static VALUE
enum_each_with_index(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo;

    RETURN_SIZED_ENUMERATOR(obj, argc, argv, enum_size);

    memo = MEMO_NEW(0, 0, 0);
    rb_block_call(obj, id_each, argc, argv, each_with_index_i, (VALUE)memo);
    return obj;
}
each_with_object(object) { |(*args), memo_object| ... } → object click to toggle source
each_with_object(object) → enumerator

Calls the block once for each element, passing both the element and the given object:

(1..4).each_with_object([]) {|i, a| a.push(i**2) } # => [1, 4, 9, 16]
h.each_with_object({}) {|element, h| k, v = *element; h[v] = k }
# => {0=>:foo, 1=>:bar, 2=>:baz}

With no block given, returns an Enumerator.

static VALUE
enum_each_with_object(VALUE obj, VALUE memo)
{
    RETURN_SIZED_ENUMERATOR(obj, 1, &memo, enum_size);

    rb_block_call(obj, id_each, 0, 0, each_with_object_i, memo);

    return memo;
}
entries(*args)

Returns an array containing the items in self:

(0..4).to_a # => [0, 1, 2, 3, 4]

Enumerable#entries is an alias for Enumerable#to_a.

Alias for: to_a
filter()

Returns an array containing elements selected by the block.

With a block given, calls the block with successive elements; returns an array of those elements for which the block returns a truthy value:

(0..9).select {|element| element % 3 == 0 } # => [0, 3, 6, 9]
a = {foo: 0, bar: 1, baz: 2}.select {|key, value| key.start_with?('b') }
a # => {:bar=>1, :baz=>2}

With no block given, returns an Enumerator.

Related: reject.

Alias for: find_all
filter_map {|element| ... } → array click to toggle source
filter_map → enumerator

Returns an array containing truthy elements returned by the block.

With a block given, calls the block with successive elements; returns an array containing each truthy value returned by the block:

(0..9).filter_map {|i| i * 2 if i.even? }                              # => [0, 4, 8, 12, 16]
{foo: 0, bar: 1, baz: 2}.filter_map {|key, value| key if value.even? } # => [:foo, :baz]

When no block given, returns an Enumerator.

static VALUE
enum_filter_map(VALUE obj)
{
    VALUE ary;

    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    ary = rb_ary_new();
    rb_block_call(obj, id_each, 0, 0, filter_map_i, ary);

    return ary;
}
find(if_none_proc = nil) {|element| ... } → object or nil click to toggle source
find(if_none_proc = nil) → enumerator

Returns the first element for which the block returns a truthy value.

With a block given, calls the block with successive elements of the collection; returns the first element for which the block returns a truthy value:

(0..9).find {|element| element > 2}                # => 3

If no such element is found, calls if_none_proc and returns its return value.

(0..9).find(proc {false}) {|element| element > 12} # => false
{foo: 0, bar: 1, baz: 2}.find {|key, value| key.start_with?('b') }            # => [:bar, 1]
{foo: 0, bar: 1, baz: 2}.find(proc {[]}) {|key, value| key.start_with?('c') } # => []

With no block given, returns an Enumerator.

static VALUE
enum_find(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo;
    VALUE if_none;

    if_none = rb_check_arity(argc, 0, 1) ? argv[0] : Qnil;
    RETURN_ENUMERATOR(obj, argc, argv);
    memo = MEMO_NEW(Qundef, 0, 0);
    rb_block_call(obj, id_each, 0, 0, find_i, (VALUE)memo);
    if (memo->u3.cnt) {
        return memo->v1;
    }
    if (!NIL_P(if_none)) {
        return rb_funcallv(if_none, id_call, 0, 0);
    }
    return Qnil;
}
Also aliased as: detect
find_all -> enumerator click to toggle source

Returns an array containing elements selected by the block.

With a block given, calls the block with successive elements; returns an array of those elements for which the block returns a truthy value:

(0..9).select {|element| element % 3 == 0 } # => [0, 3, 6, 9]
a = {foo: 0, bar: 1, baz: 2}.select {|key, value| key.start_with?('b') }
a # => {:bar=>1, :baz=>2}

With no block given, returns an Enumerator.

Related: reject.

static VALUE
enum_find_all(VALUE obj)
{
    VALUE ary;

    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    ary = rb_ary_new();
    rb_block_call(obj, id_each, 0, 0, find_all_i, ary);

    return ary;
}
Also aliased as: select, filter
find_index(object) → integer or nil click to toggle source
find_index {|element| ... } → integer or nil
find_index → enumerator

Returns the index of the first element that meets a specified criterion, or nil if no such element is found.

With argument object given, returns the index of the first element that is == object:

['a', 'b', 'c', 'b'].find_index('b') # => 1

With a block given, calls the block with successive elements; returns the first element for which the block returns a truthy value:

['a', 'b', 'c', 'b'].find_index {|element| element.start_with?('b') } # => 1
{foo: 0, bar: 1, baz: 2}.find_index {|key, value| value > 1 }         # => 2

With no argument and no block given, returns an Enumerator.

static VALUE
enum_find_index(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo;  /* [return value, current index, ] */
    VALUE condition_value = Qnil;
    rb_block_call_func *func;

    if (argc == 0) {
        RETURN_ENUMERATOR(obj, 0, 0);
        func = find_index_iter_i;
    }
    else {
        rb_scan_args(argc, argv, "1", &condition_value);
        if (rb_block_given_p()) {
            rb_warn("given block not used");
        }
        func = find_index_i;
    }

    memo = MEMO_NEW(Qnil, condition_value, 0);
    rb_block_call(obj, id_each, 0, 0, func, (VALUE)memo);
    return memo->v1;
}
first → element or nil click to toggle source
first(n) → array

Returns the first element or elements.

With no argument, returns the first element, or nil if there is none:

(1..4).first                   # => 1
%w[a b c].first                # => "a"
{foo: 1, bar: 1, baz: 2}.first # => [:foo, 1]
[].first                       # => nil

With integer argument n, returns an array containing the first n elements that exist:

(1..4).first(2)                   # => [1, 2]
%w[a b c d].first(3)              # => ["a", "b", "c"]
%w[a b c d].first(50)             # => ["a", "b", "c", "d"]
{foo: 1, bar: 1, baz: 2}.first(2) # => [[:foo, 1], [:bar, 1]]
[].first(2)                       # => []
static VALUE
enum_first(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo;
    rb_check_arity(argc, 0, 1);
    if (argc > 0) {
        return enum_take(obj, argv[0]);
    }
    else {
        memo = MEMO_NEW(Qnil, 0, 0);
        rb_block_call(obj, id_each, 0, 0, first_i, (VALUE)memo);
        return memo->v1;
    }
}
flat_map {|element| ... } → array click to toggle source
flat_map → enumerator

Returns an array of flattened objects returned by the block.

With a block given, calls the block with successive elements; returns a flattened array of objects returned by the block:

[0, 1, 2, 3].flat_map {|element| -element }                    # => [0, -1, -2, -3]
[0, 1, 2, 3].flat_map {|element| [element, -element] }         # => [0, 0, 1, -1, 2, -2, 3, -3]
[[0, 1], [2, 3]].flat_map {|e| e + [100] }                     # => [0, 1, 100, 2, 3, 100]
{foo: 0, bar: 1, baz: 2}.flat_map {|key, value| [key, value] } # => [:foo, 0, :bar, 1, :baz, 2]

With no block given, returns an Enumerator.

Alias: collect_concat.

static VALUE
enum_flat_map(VALUE obj)
{
    VALUE ary;

    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    ary = rb_ary_new();
    rb_block_call(obj, id_each, 0, 0, flat_map_i, ary);

    return ary;
}
Also aliased as: collect_concat
grep(pattern) → array click to toggle source
grep(pattern) {|element| ... } → array

Returns an array of objects based elements of self that match the given pattern.

With no block given, returns an array containing each element for which pattern === element is true:

a = ['foo', 'bar', 'car', 'moo']
a.grep(/ar/)                   # => ["bar", "car"]
(1..10).grep(3..8)             # => [3, 4, 5, 6, 7, 8]
['a', 'b', 0, 1].grep(Integer) # => [0, 1]

With a block given, calls the block with each matching element and returns an array containing each object returned by the block:

a = ['foo', 'bar', 'car', 'moo']
a.grep(/ar/) {|element| element.upcase } # => ["BAR", "CAR"]

Related: grep_v.

static VALUE
enum_grep(VALUE obj, VALUE pat)
{
    return enum_grep0(obj, pat, Qtrue);
}
grep_v(pattern) → array click to toggle source
grep_v(pattern) {|element| ... } → array

Returns an array of objects based on elements of self that don’t match the given pattern.

With no block given, returns an array containing each element for which pattern === element is false:

a = ['foo', 'bar', 'car', 'moo']
a.grep_v(/ar/)                   # => ["foo", "moo"]
(1..10).grep_v(3..8)             # => [1, 2, 9, 10]
['a', 'b', 0, 1].grep_v(Integer) # => ["a", "b"]

With a block given, calls the block with each non-matching element and returns an array containing each object returned by the block:

a = ['foo', 'bar', 'car', 'moo']
a.grep_v(/ar/) {|element| element.upcase } # => ["FOO", "MOO"]

Related: grep.

static VALUE
enum_grep_v(VALUE obj, VALUE pat)
{
    return enum_grep0(obj, pat, Qfalse);
}
group_by {|element| ... } → hash click to toggle source
group_by → enumerator

With a block given returns a hash:

  • Each key is a return value from the block.

  • Each value is an array of those elements for which the block returned that key.

Examples:

g = (1..6).group_by {|i| i%3 }
g # => {1=>[1, 4], 2=>[2, 5], 0=>[3, 6]}
h = {foo: 0, bar: 1, baz: 0, bat: 1}
g = h.group_by {|key, value| value }
g # => {0=>[[:foo, 0], [:baz, 0]], 1=>[[:bar, 1], [:bat, 1]]}

With no block given, returns an Enumerator.

static VALUE
enum_group_by(VALUE obj)
{
    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    return enum_hashify(obj, 0, 0, group_by_i);
}
include?(object) → true or false

Returns whether for any element object == element:

(1..4).include?(2)                       # => true
(1..4).include?(5)                       # => false
(1..4).include?('2')                     # => false
%w[a b c d].include?('b')                # => true
%w[a b c d].include?('2')                # => false
{foo: 0, bar: 1, baz: 2}.include?(:foo)  # => true
{foo: 0, bar: 1, baz: 2}.include?('foo') # => false
{foo: 0, bar: 1, baz: 2}.include?(0)     # => false

Enumerable#member? is an alias for Enumerable#include?.

Alias for: member?
inject(symbol) → object click to toggle source
inject(initial_operand, symbol) → object
inject {|memo, operand| ... } → object
inject(initial_operand) {|memo, operand| ... } → object

Returns an object formed from operands via either:

  • A method named by symbol.

  • A block to which each operand is passed.

With method-name argument symbol, combines operands using the method:

# Sum, without initial_operand.
(1..4).inject(:+)     # => 10
# Sum, with initial_operand.
(1..4).inject(10, :+) # => 20

With a block, passes each operand to the block:

# Sum of squares, without initial_operand.
(1..4).inject {|sum, n| sum + n*n }    # => 30
# Sum of squares, with initial_operand.
(1..4).inject(2) {|sum, n| sum + n*n } # => 32

Operands

If argument initial_operand is not given, the operands for inject are simply the elements of self. Example calls and their operands:

  • (1..4).inject(:+)

    [1, 2, 3, 4].

  • (1...4).inject(:+)

    [1, 2, 3].

  • ('a'..'d').inject(:+)

    ['a', 'b', 'c', 'd'].

  • ('a'...'d').inject(:+)

    ['a', 'b', 'c'].

Examples with first operand (which is self.first) of various types:

# Integer.
(1..4).inject(:+)                # => 10
# Float.
[1.0, 2, 3, 4].inject(:+)        # => 10.0
# Character.
('a'..'d').inject(:+)            # => "abcd"
# Complex.
[Complex(1, 2), 3, 4].inject(:+) # => (8+2i)

If argument initial_operand is given, the operands for inject are that value plus the elements of self. Example calls their operands:

  • (1..4).inject(10, :+)

    [10, 1, 2, 3, 4].

  • (1...4).inject(10, :+)

    [10, 1, 2, 3].

  • ('a'..'d').inject('e', :+)

    ['e', 'a', 'b', 'c', 'd'].

  • ('a'...'d').inject('e', :+)

    ['e', 'a', 'b', 'c'].

Examples with initial_operand of various types:

# Integer.
(1..4).inject(2, :+)               # => 12
# Float.
(1..4).inject(2.0, :+)             # => 12.0
# String.
('a'..'d').inject('foo', :+)       # => "fooabcd"
# Array.
%w[a b c].inject(['x'], :push)     # => ["x", "a", "b", "c"]
# Complex.
(1..4).inject(Complex(2, 2), :+)   # => (12+2i)

Combination by Given Method

If the method-name argument symbol is given, the operands are combined by that method:

  • The first and second operands are combined.

  • That result is combined with the third operand.

  • That result is combined with the fourth operand.

  • And so on.

The return value from inject is the result of the last combination.

This call to inject computes the sum of the operands:

(1..4).inject(:+) # => 10

Examples with various methods:

# Integer addition.
(1..4).inject(:+)                # => 10
# Integer multiplication.
(1..4).inject(:*)                # => 24
# Character range concatenation.
('a'..'d').inject('', :+)        # => "abcd"
# String array concatenation.
%w[foo bar baz].inject('', :+)   # => "foobarbaz"
# Hash update.
h = [{foo: 0, bar: 1}, {baz: 2}, {bat: 3}].inject(:update)
h # => {:foo=>0, :bar=>1, :baz=>2, :bat=>3}
# Hash conversion to nested arrays.
h = {foo: 0, bar: 1}.inject([], :push)
h # => [[:foo, 0], [:bar, 1]]

Combination by Given Block

If a block is given, the operands are passed to the block:

  • The first call passes the first and second operands.

  • The second call passes the result of the first call, along with the third operand.

  • The third call passes the result of the second call, along with the fourth operand.

  • And so on.

The return value from inject is the return value from the last block call.

This call to inject gives a block that writes the memo and element, and also sums the elements:

(1..4).inject do |memo, element|
  p "Memo: #{memo}; element: #{element}"
  memo + element
end # => 10

Output:

"Memo: 1; element: 2"
"Memo: 3; element: 3"
"Memo: 6; element: 4"

Enumerable#reduce is an alias for Enumerable#inject.

static VALUE
enum_inject(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo;
    VALUE init, op;
    rb_block_call_func *iter = inject_i;
    ID id;

    switch (rb_scan_args(argc, argv, "02", &init, &op)) {
      case 0:
        init = Qundef;
        break;
      case 1:
        if (rb_block_given_p()) {
            break;
        }
        id = rb_check_id(&init);
        op = id ? ID2SYM(id) : init;
        init = Qundef;
        iter = inject_op_i;
        break;
      case 2:
        if (rb_block_given_p()) {
            rb_warning("given block not used");
        }
        id = rb_check_id(&op);
        if (id) op = ID2SYM(id);
        iter = inject_op_i;
        break;
    }

    if (iter == inject_op_i &&
        SYMBOL_P(op) &&
        RB_TYPE_P(obj, T_ARRAY) &&
        rb_method_basic_definition_p(CLASS_OF(obj), id_each)) {
        return ary_inject_op(obj, init, op);
    }

    memo = MEMO_NEW(init, Qnil, op);
    rb_block_call(obj, id_each, 0, 0, iter, (VALUE)memo);
    if (memo->v1 == Qundef) return Qnil;
    return memo->v1;
}
Also aliased as: reduce
lazy → lazy_enumerator click to toggle source

Returns an Enumerator::Lazy, which redefines most Enumerable methods to postpone enumeration and enumerate values only on an as-needed basis.

Example

The following program finds pythagorean triples:

def pythagorean_triples
  (1..Float::INFINITY).lazy.flat_map {|z|
    (1..z).flat_map {|x|
      (x..z).select {|y|
        x**2 + y**2 == z**2
      }.map {|y|
        [x, y, z]
      }
    }
  }
end
# show first ten pythagorean triples
p pythagorean_triples.take(10).force # take is lazy, so force is needed
p pythagorean_triples.first(10)      # first is eager
# show pythagorean triples less than 100
p pythagorean_triples.take_while { |*, z| z < 100 }.force
static VALUE
enumerable_lazy(VALUE obj)
{
    VALUE result = lazy_to_enum_i(obj, sym_each, 0, 0, lazyenum_size, rb_keyword_given_p());
    /* Qfalse indicates that the Enumerator::Lazy has no method name */
    rb_ivar_set(result, id_method, Qfalse);
    return result;
}
map {|element| ... } → array
map → enumerator

Returns an array of objects returned by the block.

With a block given, calls the block with successive elements; returns an array of the objects returned by the block:

(0..4).map {|i| i*i }                               # => [0, 1, 4, 9, 16]
{foo: 0, bar: 1, baz: 2}.map {|key, value| value*2} # => [0, 2, 4]

With no block given, returns an Enumerator.

Alias for: collect
max → element click to toggle source
max(n) → array
max {|a, b| ... } → element
max(n) {|a, b| ... } → array

Returns the element with the maximum element according to a given criterion. The ordering of equal elements is indeterminate and may be unstable.

With no argument and no block, returns the maximum element, using the elements’ own method <=> for comparison:

(1..4).max                   # => 4
(-4..-1).max                 # => -1
%w[d c b a].max              # => "d"
{foo: 0, bar: 1, baz: 2}.max # => [:foo, 0]
[].max                       # => nil

With positive integer argument n given, and no block, returns an array containing the first n maximum elements that exist:

(1..4).max(2)                   # => [4, 3]
(-4..-1).max(2)                # => [-1, -2]
%w[d c b a].max(2)              # => ["d", "c"]
{foo: 0, bar: 1, baz: 2}.max(2) # => [[:foo, 0], [:baz, 2]]
[].max(2)                       # => []

With a block given, the block determines the maximum elements. The block is called with two elements a and b, and must return:

  • A negative integer if a < b.

  • Zero if a == b.

  • A positive integer if a > b.

With a block given and no argument, returns the maximum element as determined by the block:

%w[xxx x xxxx xx].max {|a, b| a.size <=> b.size } # => "xxxx"
h = {foo: 0, bar: 1, baz: 2}
h.max {|pair1, pair2| pair1[1] <=> pair2[1] }     # => [:baz, 2]
[].max {|a, b| a <=> b }                          # => nil

With a block given and positive integer argument n given, returns an array containing the first n maximum elements that exist, as determined by the block.

%w[xxx x xxxx xx].max(2) {|a, b| a.size <=> b.size } # => ["xxxx", "xxx"]
h = {foo: 0, bar: 1, baz: 2}
h.max(2) {|pair1, pair2| pair1[1] <=> pair2[1] }
# => [[:baz, 2], [:bar, 1]]
[].max(2) {|a, b| a <=> b }                          # => []

Related: min, minmax, max_by.

static VALUE
enum_max(int argc, VALUE *argv, VALUE obj)
{
    VALUE memo;
    struct max_t *m = NEW_CMP_OPT_MEMO(struct max_t, memo);
    VALUE result;
    VALUE num;

    if (rb_check_arity(argc, 0, 1) && !NIL_P(num = argv[0]))
       return rb_nmin_run(obj, num, 0, 1, 0);

    m->max = Qundef;
    m->cmp_opt.opt_methods = 0;
    m->cmp_opt.opt_inited = 0;
    if (rb_block_given_p()) {
        rb_block_call(obj, id_each, 0, 0, max_ii, (VALUE)memo);
    }
    else {
        rb_block_call(obj, id_each, 0, 0, max_i, (VALUE)memo);
    }
    result = m->max;
    if (result == Qundef) return Qnil;
    return result;
}
max_by {|element| ... } → element click to toggle source
max_by(n) {|element| ... } → array
max_by → enumerator
max_by(n) → enumerator

Returns the elements for which the block returns the maximum values.

With a block given and no argument, returns the element for which the block returns the maximum value:

(1..4).max_by {|element| -element }                    # => 1
%w[a b c d].max_by {|element| -element.ord }           # => "a"
{foo: 0, bar: 1, baz: 2}.max_by {|key, value| -value } # => [:foo, 0]
[].max_by {|element| -element }                        # => nil

With a block given and positive integer argument n given, returns an array containing the n elements for which the block returns maximum values:

(1..4).max_by(2) {|element| -element }
# => [1, 2]
%w[a b c d].max_by(2) {|element| -element.ord }
# => ["a", "b"]
{foo: 0, bar: 1, baz: 2}.max_by(2) {|key, value| -value }
# => [[:foo, 0], [:bar, 1]]
[].max_by(2) {|element| -element }
# => []

Returns an Enumerator if no block is given.

Related: max, minmax, min_by.

static VALUE
enum_max_by(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo;
    VALUE num;

    rb_check_arity(argc, 0, 1);

    RETURN_SIZED_ENUMERATOR(obj, argc, argv, enum_size);

    if (argc && !NIL_P(num = argv[0]))
        return rb_nmin_run(obj, num, 1, 1, 0);

    memo = MEMO_NEW(Qundef, Qnil, 0);
    rb_block_call(obj, id_each, 0, 0, max_by_i, (VALUE)memo);
    return memo->v2;
}
member?(object) -> true or false click to toggle source

Returns whether for any element object == element:

(1..4).include?(2)                       # => true
(1..4).include?(5)                       # => false
(1..4).include?('2')                     # => false
%w[a b c d].include?('b')                # => true
%w[a b c d].include?('2')                # => false
{foo: 0, bar: 1, baz: 2}.include?(:foo)  # => true
{foo: 0, bar: 1, baz: 2}.include?('foo') # => false
{foo: 0, bar: 1, baz: 2}.include?(0)     # => false

Enumerable#member? is an alias for Enumerable#include?.

static VALUE
enum_member(VALUE obj, VALUE val)
{
    struct MEMO *memo = MEMO_NEW(val, Qfalse, 0);

    rb_block_call(obj, id_each, 0, 0, member_i, (VALUE)memo);
    return memo->v2;
}
Also aliased as: include?
min → element click to toggle source
min(n) → array
min {|a, b| ... } → element
min(n) {|a, b| ... } → array

Returns the element with the minimum element according to a given criterion. The ordering of equal elements is indeterminate and may be unstable.

With no argument and no block, returns the minimum element, using the elements’ own method <=> for comparison:

(1..4).min                   # => 1
(-4..-1).min                 # => -4
%w[d c b a].min              # => "a"
{foo: 0, bar: 1, baz: 2}.min # => [:bar, 1]
[].min                       # => nil

With positive integer argument n given, and no block, returns an array containing the first n minimum elements that exist:

(1..4).min(2)                   # => [1, 2]
(-4..-1).min(2)                 # => [-4, -3]
%w[d c b a].min(2)              # => ["a", "b"]
{foo: 0, bar: 1, baz: 2}.min(2) # => [[:bar, 1], [:baz, 2]]
[].min(2)                       # => []

With a block given, the block determines the minimum elements. The block is called with two elements a and b, and must return:

  • A negative integer if a < b.

  • Zero if a == b.

  • A positive integer if a > b.

With a block given and no argument, returns the minimum element as determined by the block:

%w[xxx x xxxx xx].min {|a, b| a.size <=> b.size } # => "x"
h = {foo: 0, bar: 1, baz: 2}
h.min {|pair1, pair2| pair1[1] <=> pair2[1] } # => [:foo, 0]
[].min {|a, b| a <=> b }                          # => nil

With a block given and positive integer argument n given, returns an array containing the first n minimum elements that exist, as determined by the block.

%w[xxx x xxxx xx].min(2) {|a, b| a.size <=> b.size } # => ["x", "xx"]
h = {foo: 0, bar: 1, baz: 2}
h.min(2) {|pair1, pair2| pair1[1] <=> pair2[1] }
# => [[:foo, 0], [:bar, 1]]
[].min(2) {|a, b| a <=> b }                          # => []

Related: min_by, minmax, max.

static VALUE
enum_min(int argc, VALUE *argv, VALUE obj)
{
    VALUE memo;
    struct min_t *m = NEW_CMP_OPT_MEMO(struct min_t, memo);
    VALUE result;
    VALUE num;

    if (rb_check_arity(argc, 0, 1) && !NIL_P(num = argv[0]))
       return rb_nmin_run(obj, num, 0, 0, 0);

    m->min = Qundef;
    m->cmp_opt.opt_methods = 0;
    m->cmp_opt.opt_inited = 0;
    if (rb_block_given_p()) {
        rb_block_call(obj, id_each, 0, 0, min_ii, memo);
    }
    else {
        rb_block_call(obj, id_each, 0, 0, min_i, memo);
    }
    result = m->min;
    if (result == Qundef) return Qnil;
    return result;
}
min_by {|element| ... } → element click to toggle source
min_by(n) {|element| ... } → array
min_by → enumerator
min_by(n) → enumerator

Returns the elements for which the block returns the minimum values.

With a block given and no argument, returns the element for which the block returns the minimum value:

(1..4).min_by {|element| -element }                    # => 4
%w[a b c d].min_by {|element| -element.ord }           # => "d"
{foo: 0, bar: 1, baz: 2}.min_by {|key, value| -value } # => [:baz, 2]
[].min_by {|element| -element }                        # => nil

With a block given and positive integer argument n given, returns an array containing the n elements for which the block returns minimum values:

(1..4).min_by(2) {|element| -element }
# => [4, 3]
%w[a b c d].min_by(2) {|element| -element.ord }
# => ["d", "c"]
{foo: 0, bar: 1, baz: 2}.min_by(2) {|key, value| -value }
# => [[:baz, 2], [:bar, 1]]
[].min_by(2) {|element| -element }
# => []

Returns an Enumerator if no block is given.

Related: min, minmax, max_by.

static VALUE
enum_min_by(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo;
    VALUE num;

    rb_check_arity(argc, 0, 1);

    RETURN_SIZED_ENUMERATOR(obj, argc, argv, enum_size);

    if (argc && !NIL_P(num = argv[0]))
        return rb_nmin_run(obj, num, 1, 0, 0);

    memo = MEMO_NEW(Qundef, Qnil, 0);
    rb_block_call(obj, id_each, 0, 0, min_by_i, (VALUE)memo);
    return memo->v2;
}
minmax → [minimum, maximum] click to toggle source
minmax {|a, b| ... } → [minimum, maximum]

Returns a 2-element array containing the minimum and maximum elements according to a given criterion. The ordering of equal elements is indeterminate and may be unstable.

With no argument and no block, returns the minimum and maximum elements, using the elements’ own method <=> for comparison:

(1..4).minmax                   # => [1, 4]
(-4..-1).minmax                 # => [-4, -1]
%w[d c b a].minmax              # => ["a", "d"]
{foo: 0, bar: 1, baz: 2}.minmax # => [[:bar, 1], [:foo, 0]]
[].minmax                       # => [nil, nil]

With a block given, returns the minimum and maximum elements as determined by the block:

%w[xxx x xxxx xx].minmax {|a, b| a.size <=> b.size } # => ["x", "xxxx"]
h = {foo: 0, bar: 1, baz: 2}
h.minmax {|pair1, pair2| pair1[1] <=> pair2[1] }
# => [[:foo, 0], [:baz, 2]]
[].minmax {|a, b| a <=> b }                          # => [nil, nil]

Related: min, max, minmax_by.

static VALUE
enum_minmax(VALUE obj)
{
    VALUE memo;
    struct minmax_t *m = NEW_CMP_OPT_MEMO(struct minmax_t, memo);

    m->min = Qundef;
    m->last = Qundef;
    m->cmp_opt.opt_methods = 0;
    m->cmp_opt.opt_inited = 0;
    if (rb_block_given_p()) {
        rb_block_call(obj, id_each, 0, 0, minmax_ii, memo);
        if (m->last != Qundef)
            minmax_ii_update(m->last, m->last, m);
    }
    else {
        rb_block_call(obj, id_each, 0, 0, minmax_i, memo);
        if (m->last != Qundef)
            minmax_i_update(m->last, m->last, m);
    }
    if (m->min != Qundef) {
        return rb_assoc_new(m->min, m->max);
    }
    return rb_assoc_new(Qnil, Qnil);
}
minmax_by {|element| ... } → [minimum, maximum] click to toggle source
minmax_by → enumerator

Returns a 2-element array containing the elements for which the block returns minimum and maximum values:

(1..4).minmax_by {|element| -element }
# => [4, 1]
%w[a b c d].minmax_by {|element| -element.ord }
# => ["d", "a"]
{foo: 0, bar: 1, baz: 2}.minmax_by {|key, value| -value }
# => [[:baz, 2], [:foo, 0]]
[].minmax_by {|element| -element }
# => [nil, nil]

Returns an Enumerator if no block is given.

Related: max_by, minmax, min_by.

static VALUE
enum_minmax_by(VALUE obj)
{
    VALUE memo;
    struct minmax_by_t *m = NEW_MEMO_FOR(struct minmax_by_t, memo);

    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    m->min_bv = Qundef;
    m->max_bv = Qundef;
    m->min = Qnil;
    m->max = Qnil;
    m->last_bv = Qundef;
    m->last = Qundef;
    rb_block_call(obj, id_each, 0, 0, minmax_by_i, memo);
    if (m->last_bv != Qundef)
        minmax_by_i_update(m->last_bv, m->last_bv, m->last, m->last, m);
    m = MEMO_FOR(struct minmax_by_t, memo);
    return rb_assoc_new(m->min, m->max);
}
none? → true or false click to toggle source
none?(pattern) → true or false
none? {|element| ... } → true or false

Returns whether no element meets a given criterion.

With no argument and no block, returns whether no element is truthy:

(1..4).none?           # => false
[nil, false].none?     # => true
{foo: 0}.none?         # => false
{foo: 0, bar: 1}.none? # => false
[].none?               # => true

With argument pattern and no block, returns whether for no element element, pattern === element:

[nil, false, 1.1].none?(Integer)      # => true
%w[bar baz bat bam].none?(/m/)        # => false
%w[bar baz bat bam].none?(/foo/)      # => true
%w[bar baz bat bam].none?('ba')       # => true
{foo: 0, bar: 1, baz: 2}.none?(Hash)  # => true
{foo: 0}.none?(Array)                 # => false
[].none?(Integer)                     # => true

With a block given, returns whether the block returns a truthy value for no element:

(1..4).none? {|element| element < 1 }                     # => true
(1..4).none? {|element| element < 2 }                     # => false
{foo: 0, bar: 1, baz: 2}.none? {|key, value| value < 0 }  # => true
{foo: 0, bar: 1, baz: 2}.none? {|key, value| value < 1 } # => false

Related: one?, all?, any?.

static VALUE
enum_none(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo = MEMO_ENUM_NEW(Qtrue);

    WARN_UNUSED_BLOCK(argc);
    rb_block_call(obj, id_each, 0, 0, ENUMFUNC(none), (VALUE)memo);
    return memo->v1;
}
one? → true or false click to toggle source
one?(pattern) → true or false
one? {|element| ... } → true or false

Returns whether exactly one element meets a given criterion.

With no argument and no block, returns whether exactly one element is truthy:

(1..1).one?           # => true
[1, nil, false].one?  # => true
(1..4).one?           # => false
{foo: 0}.one?         # => true
{foo: 0, bar: 1}.one? # => false
[].one?               # => false

With argument pattern and no block, returns whether for exactly one element element, pattern === element:

[nil, false, 0].one?(Integer)        # => true
[nil, false, 0].one?(Numeric)        # => true
[nil, false, 0].one?(Float)          # => false
%w[bar baz bat bam].one?(/m/)        # => true
%w[bar baz bat bam].one?(/foo/)      # => false
%w[bar baz bat bam].one?('ba')       # => false
{foo: 0, bar: 1, baz: 2}.one?(Array) # => false
{foo: 0}.one?(Array)                 # => true
[].one?(Integer)                     # => false

With a block given, returns whether the block returns a truthy value for exactly one element:

(1..4).one? {|element| element < 2 }                     # => true
(1..4).one? {|element| element < 1 }                     # => false
{foo: 0, bar: 1, baz: 2}.one? {|key, value| value < 1 }  # => true
{foo: 0, bar: 1, baz: 2}.one? {|key, value| value < 2 } # => false

Related: none?, all?, any?.

static VALUE
enum_one(int argc, VALUE *argv, VALUE obj)
{
    struct MEMO *memo = MEMO_ENUM_NEW(Qundef);
    VALUE result;

    WARN_UNUSED_BLOCK(argc);
    rb_block_call(obj, id_each, 0, 0, ENUMFUNC(one), (VALUE)memo);
    result = memo->v1;
    if (result == Qundef) return Qfalse;
    return result;
}
partition {|element| ... } → [true_array, false_array] click to toggle source
partition → enumerator

With a block given, returns an array of two arrays:

  • The first having those elements for which the block returns a truthy value.

  • The other having all other elements.

Examples:

p = (1..4).partition {|i| i.even? }
p # => [[2, 4], [1, 3]]
p = ('a'..'d').partition {|c| c < 'c' }
p # => [["a", "b"], ["c", "d"]]
h = {foo: 0, bar: 1, baz: 2, bat: 3}
p = h.partition {|key, value| key.start_with?('b') }
p # => [[[:bar, 1], [:baz, 2], [:bat, 3]], [[:foo, 0]]]
p = h.partition {|key, value| value < 2 }
p # => [[[:foo, 0], [:bar, 1]], [[:baz, 2], [:bat, 3]]]

With no block given, returns an Enumerator.

Related: Enumerable#group_by.

static VALUE
enum_partition(VALUE obj)
{
    struct MEMO *memo;

    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    memo = MEMO_NEW(rb_ary_new(), rb_ary_new(), 0);
    rb_block_call(obj, id_each, 0, 0, partition_i, (VALUE)memo);

    return rb_assoc_new(memo->v1, memo->v2);
}
reduce(p1 = v1, p2 = v2)

Returns an object formed from operands via either:

  • A method named by symbol.

  • A block to which each operand is passed.

With method-name argument symbol, combines operands using the method:

# Sum, without initial_operand.
(1..4).inject(:+)     # => 10
# Sum, with initial_operand.
(1..4).inject(10, :+) # => 20

With a block, passes each operand to the block:

# Sum of squares, without initial_operand.
(1..4).inject {|sum, n| sum + n*n }    # => 30
# Sum of squares, with initial_operand.
(1..4).inject(2) {|sum, n| sum + n*n } # => 32

Operands

If argument initial_operand is not given, the operands for inject are simply the elements of self. Example calls and their operands:

  • (1..4).inject(:+)

    [1, 2, 3, 4].

  • (1...4).inject(:+)

    [1, 2, 3].

  • ('a'..'d').inject(:+)

    ['a', 'b', 'c', 'd'].

  • ('a'...'d').inject(:+)

    ['a', 'b', 'c'].

Examples with first operand (which is self.first) of various types:

# Integer.
(1..4).inject(:+)                # => 10
# Float.
[1.0, 2, 3, 4].inject(:+)        # => 10.0
# Character.
('a'..'d').inject(:+)            # => "abcd"
# Complex.
[Complex(1, 2), 3, 4].inject(:+) # => (8+2i)

If argument initial_operand is given, the operands for inject are that value plus the elements of self. Example calls their operands:

  • (1..4).inject(10, :+)

    [10, 1, 2, 3, 4].

  • (1...4).inject(10, :+)

    [10, 1, 2, 3].

  • ('a'..'d').inject('e', :+)

    ['e', 'a', 'b', 'c', 'd'].

  • ('a'...'d').inject('e', :+)

    ['e', 'a', 'b', 'c'].

Examples with initial_operand of various types:

# Integer.
(1..4).inject(2, :+)               # => 12
# Float.
(1..4).inject(2.0, :+)             # => 12.0
# String.
('a'..'d').inject('foo', :+)       # => "fooabcd"
# Array.
%w[a b c].inject(['x'], :push)     # => ["x", "a", "b", "c"]
# Complex.
(1..4).inject(Complex(2, 2), :+)   # => (12+2i)

Combination by Given Method

If the method-name argument symbol is given, the operands are combined by that method:

  • The first and second operands are combined.

  • That result is combined with the third operand.

  • That result is combined with the fourth operand.

  • And so on.

The return value from inject is the result of the last combination.

This call to inject computes the sum of the operands:

(1..4).inject(:+) # => 10

Examples with various methods:

# Integer addition.
(1..4).inject(:+)                # => 10
# Integer multiplication.
(1..4).inject(:*)                # => 24
# Character range concatenation.
('a'..'d').inject('', :+)        # => "abcd"
# String array concatenation.
%w[foo bar baz].inject('', :+)   # => "foobarbaz"
# Hash update.
h = [{foo: 0, bar: 1}, {baz: 2}, {bat: 3}].inject(:update)
h # => {:foo=>0, :bar=>1, :baz=>2, :bat=>3}
# Hash conversion to nested arrays.
h = {foo: 0, bar: 1}.inject([], :push)
h # => [[:foo, 0], [:bar, 1]]

Combination by Given Block

If a block is given, the operands are passed to the block:

  • The first call passes the first and second operands.

  • The second call passes the result of the first call, along with the third operand.

  • The third call passes the result of the second call, along with the fourth operand.

  • And so on.

The return value from inject is the return value from the last block call.

This call to inject gives a block that writes the memo and element, and also sums the elements:

(1..4).inject do |memo, element|
  p "Memo: #{memo}; element: #{element}"
  memo + element
end # => 10

Output:

"Memo: 1; element: 2"
"Memo: 3; element: 3"
"Memo: 6; element: 4"

Enumerable#reduce is an alias for Enumerable#inject.

Alias for: inject
reject {|element| ... } → array click to toggle source
reject → enumerator

Returns an array of objects rejected by the block.

With a block given, calls the block with successive elements; returns an array of those elements for which the block returns nil or false:

(0..9).reject {|i| i * 2 if i.even? }                             # => [1, 3, 5, 7, 9]
{foo: 0, bar: 1, baz: 2}.reject {|key, value| key if value.odd? } # => {:foo=>0, :baz=>2}

When no block given, returns an Enumerator.

Related: select.

static VALUE
enum_reject(VALUE obj)
{
    VALUE ary;

    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    ary = rb_ary_new();
    rb_block_call(obj, id_each, 0, 0, reject_i, ary);

    return ary;
}
reverse_each(*args) {|element| ... } → self click to toggle source
reverse_each(*args) → enumerator

With a block given, calls the block with each element, but in reverse order; returns self:

a = []
(1..4).reverse_each {|element| a.push(-element) } # => 1..4
a # => [-4, -3, -2, -1]

a = []
%w[a b c d].reverse_each {|element| a.push(element) }
# => ["a", "b", "c", "d"]
a # => ["d", "c", "b", "a"]

a = []
h.reverse_each {|element| a.push(element) }
# => {:foo=>0, :bar=>1, :baz=>2}
a # => [[:baz, 2], [:bar, 1], [:foo, 0]]

With no block given, returns an Enumerator.

static VALUE
enum_reverse_each(int argc, VALUE *argv, VALUE obj)
{
    VALUE ary;
    long len;

    RETURN_SIZED_ENUMERATOR(obj, argc, argv, enum_size);

    ary = enum_to_a(argc, argv, obj);

    len = RARRAY_LEN(ary);
    while (len--) {
        long nlen;
        rb_yield(RARRAY_AREF(ary, len));
        nlen = RARRAY_LEN(ary);
        if (nlen < len) {
            len = nlen;
        }
    }

    return obj;
}
select {|element| ... } → array
select → enumerator

Returns an array containing elements selected by the block.

With a block given, calls the block with successive elements; returns an array of those elements for which the block returns a truthy value:

(0..9).select {|element| element % 3 == 0 } # => [0, 3, 6, 9]
a = {foo: 0, bar: 1, baz: 2}.select {|key, value| key.start_with?('b') }
a # => {:bar=>1, :baz=>2}

With no block given, returns an Enumerator.

Related: reject.

Alias for: find_all
slice_after(pattern) → enumerator click to toggle source
slice_after {|array| ... } → enumerator

With argument pattern, returns an enumerator that uses the pattern to partition elements into arrays (“slices”). An element ends the current slice if element === pattern:

a = %w[foo bar fop for baz fob fog bam foy]
e = a.slice_after(/ba/) # => #<Enumerator: ...>
e.each {|array| p array }

Output:

["foo", "bar"]
["fop", "for", "baz"]
["fob", "fog", "bam"]
["foy"]

With a block, returns an enumerator that uses the block to partition elements into arrays. An element ends the current slice if its block return is a truthy value:

e = (1..20).slice_after {|i| i % 4 == 2 } # => #<Enumerator: ...>
e.each {|array| p array }

Output:

[1, 2]
[3, 4, 5, 6]
[7, 8, 9, 10]
[11, 12, 13, 14]
[15, 16, 17, 18]
[19, 20]

Other methods of the Enumerator class and Enumerable module, such as map, etc., are also usable.

For example, continuation lines (lines end with backslash) can be concatenated as follows:

lines = ["foo\n", "bar\\\n", "baz\n", "\n", "qux\n"]
e = lines.slice_after(/(?<!\\)\n\z/)
p e.to_a
#=> [["foo\n"], ["bar\\\n", "baz\n"], ["\n"], ["qux\n"]]
p e.map {|ll| ll[0...-1].map {|l| l.sub(/\\\n\z/, "") }.join + ll.last }
#=>["foo\n", "barbaz\n", "\n", "qux\n"]
static VALUE
enum_slice_after(int argc, VALUE *argv, VALUE enumerable)
{
    VALUE enumerator;
    VALUE pat = Qnil, pred = Qnil;

    if (rb_block_given_p()) {
        if (0 < argc)
            rb_raise(rb_eArgError, "both pattern and block are given");
        pred = rb_block_proc();
    }
    else {
        rb_scan_args(argc, argv, "1", &pat);
    }

    enumerator = rb_obj_alloc(rb_cEnumerator);
    rb_ivar_set(enumerator, id_sliceafter_enum, enumerable);
    rb_ivar_set(enumerator, id_sliceafter_pat, pat);
    rb_ivar_set(enumerator, id_sliceafter_pred, pred);

    rb_block_call(enumerator, idInitialize, 0, 0, sliceafter_i, enumerator);
    return enumerator;
}
slice_before(pattern) → enumerator click to toggle source
slice_before {|array| ... } → enumerator

With argument pattern, returns an enumerator that uses the pattern to partition elements into arrays (“slices”). An element begins a new slice if element === pattern (or if it is the first element).

a = %w[foo bar fop for baz fob fog bam foy]
e = a.slice_before(/ba/) # => #<Enumerator: ...>
e.each {|array| p array }

Output:

["foo"]
["bar", "fop", "for"]
["baz", "fob", "fog"]
["bam", "foy"]

With a block, returns an enumerator that uses the block to partition elements into arrays. An element begins a new slice if its block return is a truthy value (or if it is the first element):

e = (1..20).slice_before {|i| i % 4 == 2 } # => #<Enumerator: ...>
e.each {|array| p array }

Output:

[1]
[2, 3, 4, 5]
[6, 7, 8, 9]
[10, 11, 12, 13]
[14, 15, 16, 17]
[18, 19, 20]

Other methods of the Enumerator class and Enumerable module, such as to_a, map, etc., are also usable.

For example, iteration over ChangeLog entries can be implemented as follows:

# iterate over ChangeLog entries.
open("ChangeLog") { |f|
  f.slice_before(/\A\S/).each { |e| pp e }
}

# same as above.  block is used instead of pattern argument.
open("ChangeLog") { |f|
  f.slice_before { |line| /\A\S/ === line }.each { |e| pp e }
}

“svn proplist -R” produces multiline output for each file. They can be chunked as follows:

IO.popen([{"LC_ALL"=>"C"}, "svn", "proplist", "-R"]) { |f|
  f.lines.slice_before(/\AProp/).each { |lines| p lines }
}
#=> ["Properties on '.':\n", "  svn:ignore\n", "  svk:merge\n"]
#   ["Properties on 'goruby.c':\n", "  svn:eol-style\n"]
#   ["Properties on 'complex.c':\n", "  svn:mime-type\n", "  svn:eol-style\n"]
#   ["Properties on 'regparse.c':\n", "  svn:eol-style\n"]
#   ...

If the block needs to maintain state over multiple elements, local variables can be used. For example, three or more consecutive increasing numbers can be squashed as follows (see chunk_while for a better way):

a = [0, 2, 3, 4, 6, 7, 9]
prev = a[0]
p a.slice_before { |e|
  prev, prev2 = e, prev
  prev2 + 1 != e
}.map { |es|
  es.length <= 2 ? es.join(",") : "#{es.first}-#{es.last}"
}.join(",")
#=> "0,2-4,6,7,9"

However local variables should be used carefully if the result enumerator is enumerated twice or more. The local variables should be initialized for each enumeration. Enumerator.new can be used to do it.

# Word wrapping.  This assumes all characters have same width.
def wordwrap(words, maxwidth)
  Enumerator.new {|y|
    # cols is initialized in Enumerator.new.
    cols = 0
    words.slice_before { |w|
      cols += 1 if cols != 0
      cols += w.length
      if maxwidth < cols
        cols = w.length
        true
      else
        false
      end
    }.each {|ws| y.yield ws }
  }
end
text = (1..20).to_a.join(" ")
enum = wordwrap(text.split(/\s+/), 10)
puts "-"*10
enum.each { |ws| puts ws.join(" ") } # first enumeration.
puts "-"*10
enum.each { |ws| puts ws.join(" ") } # second enumeration generates same result as the first.
puts "-"*10
#=> ----------
#   1 2 3 4 5
#   6 7 8 9 10
#   11 12 13
#   14 15 16
#   17 18 19
#   20
#   ----------
#   1 2 3 4 5
#   6 7 8 9 10
#   11 12 13
#   14 15 16
#   17 18 19
#   20
#   ----------

mbox contains series of mails which start with Unix From line. So each mail can be extracted by slice before Unix From line.

# parse mbox
open("mbox") { |f|
  f.slice_before { |line|
    line.start_with? "From "
  }.each { |mail|
    unix_from = mail.shift
    i = mail.index("\n")
    header = mail[0...i]
    body = mail[(i+1)..-1]
    body.pop if body.last == "\n"
    fields = header.slice_before { |line| !" \t".include?(line[0]) }.to_a
    p unix_from
    pp fields
    pp body
  }
}

# split mails in mbox (slice before Unix From line after an empty line)
open("mbox") { |f|
  emp = true
  f.slice_before { |line|
    prevemp = emp
    emp = line == "\n"
    prevemp && line.start_with?("From ")
  }.each { |mail|
    mail.pop if mail.last == "\n"
    pp mail
  }
}
static VALUE
enum_slice_before(int argc, VALUE *argv, VALUE enumerable)
{
    VALUE enumerator;

    if (rb_block_given_p()) {
        if (argc != 0)
            rb_error_arity(argc, 0, 0);
        enumerator = rb_obj_alloc(rb_cEnumerator);
        rb_ivar_set(enumerator, id_slicebefore_sep_pred, rb_block_proc());
    }
    else {
        VALUE sep_pat;
        rb_scan_args(argc, argv, "1", &sep_pat);
        enumerator = rb_obj_alloc(rb_cEnumerator);
        rb_ivar_set(enumerator, id_slicebefore_sep_pat, sep_pat);
    }
    rb_ivar_set(enumerator, id_slicebefore_enumerable, enumerable);
    rb_block_call(enumerator, idInitialize, 0, 0, slicebefore_i, enumerator);
    return enumerator;
}
slice_when {|element, next_element| ... } → enumerator click to toggle source

The returned enumerator uses the block to partition elements into arrays (“slices”); it calls the block with each element and its successor; begins a new slice if and only if the block returns a truthy value:

a = [0, 1, 2, 4, 5, 6, 8, 9]
e = a.slice_when {|i, j| j != i + 1 }
e.each {|array| p array }

Output:

[0, 1, 2]
[4, 5, 6]
[8, 9]
static VALUE
enum_slice_when(VALUE enumerable)
{
    VALUE enumerator;
    VALUE pred;

    pred = rb_block_proc();

    enumerator = rb_obj_alloc(rb_cEnumerator);
    rb_ivar_set(enumerator, id_slicewhen_enum, enumerable);
    rb_ivar_set(enumerator, id_slicewhen_pred, pred);
    rb_ivar_set(enumerator, id_slicewhen_inverted, Qfalse);

    rb_block_call(enumerator, idInitialize, 0, 0, slicewhen_i, enumerator);
    return enumerator;
}
sort → array click to toggle source
sort {|a, b| ... } → array

Returns an array containing the sorted elements of self. The ordering of equal elements is indeterminate and may be unstable.

With no block given, the sort compares using the elements’ own method <=>:

%w[b c a d].sort              # => ["a", "b", "c", "d"]
{foo: 0, bar: 1, baz: 2}.sort # => [[:bar, 1], [:baz, 2], [:foo, 0]]

With a block given, comparisons in the block determine the ordering. The block is called with two elements a and b, and must return:

  • A negative integer if a < b.

  • Zero if a == b.

  • A positive integer if a > b.

Examples:

a = %w[b c a d]
a.sort {|a, b| b <=> a } # => ["d", "c", "b", "a"]
h = {foo: 0, bar: 1, baz: 2}
h.sort {|a, b| b <=> a } # => [[:foo, 0], [:baz, 2], [:bar, 1]]

See also sort_by. It implements a Schwartzian transform which is useful when key computation or comparison is expensive.

static VALUE
enum_sort(VALUE obj)
{
    return rb_ary_sort_bang(enum_to_a(0, 0, obj));
}
sort_by {|element| ... } → array click to toggle source
sort_by → enumerator

With a block given, returns an array of elements of self, sorted according to the value returned by the block for each element. The ordering of equal elements is indeterminate and may be unstable.

Examples:

a = %w[xx xxx x xxxx]
a.sort_by {|s| s.size }        # => ["x", "xx", "xxx", "xxxx"]
a.sort_by {|s| -s.size }       # => ["xxxx", "xxx", "xx", "x"]
h = {foo: 2, bar: 1, baz: 0}
h.sort_by{|key, value| value } # => [[:baz, 0], [:bar, 1], [:foo, 2]]
h.sort_by{|key, value| key }   # => [[:bar, 1], [:baz, 0], [:foo, 2]]

With no block given, returns an Enumerator.

The current implementation of sort_by generates an array of tuples containing the original collection element and the mapped value. This makes sort_by fairly expensive when the keysets are simple.

require 'benchmark'

a = (1..100000).map { rand(100000) }

Benchmark.bm(10) do |b|
  b.report("Sort")    { a.sort }
  b.report("Sort by") { a.sort_by { |a| a } }
end

produces:

user     system      total        real
Sort        0.180000   0.000000   0.180000 (  0.175469)
Sort by     1.980000   0.040000   2.020000 (  2.013586)

However, consider the case where comparing the keys is a non-trivial operation. The following code sorts some files on modification time using the basic sort method.

files = Dir["*"]
sorted = files.sort { |a, b| File.new(a).mtime <=> File.new(b).mtime }
sorted   #=> ["mon", "tues", "wed", "thurs"]

This sort is inefficient: it generates two new File objects during every comparison. A slightly better technique is to use the Kernel#test method to generate the modification times directly.

files = Dir["*"]
sorted = files.sort { |a, b|
  test(?M, a) <=> test(?M, b)
}
sorted   #=> ["mon", "tues", "wed", "thurs"]

This still generates many unnecessary Time objects. A more efficient technique is to cache the sort keys (modification times in this case) before the sort. Perl users often call this approach a Schwartzian transform, after Randal Schwartz. We construct a temporary array, where each element is an array containing our sort key along with the filename. We sort this array, and then extract the filename from the result.

sorted = Dir["*"].collect { |f|
   [test(?M, f), f]
}.sort.collect { |f| f[1] }
sorted   #=> ["mon", "tues", "wed", "thurs"]

This is exactly what sort_by does internally.

sorted = Dir["*"].sort_by { |f| test(?M, f) }
sorted   #=> ["mon", "tues", "wed", "thurs"]

To produce the reverse of a specific order, the following can be used:

ary.sort_by { ... }.reverse!
static VALUE
enum_sort_by(VALUE obj)
{
    VALUE ary, buf;
    struct MEMO *memo;
    long i;
    struct sort_by_data *data;

    RETURN_SIZED_ENUMERATOR(obj, 0, 0, enum_size);

    if (RB_TYPE_P(obj, T_ARRAY) && RARRAY_LEN(obj) <= LONG_MAX/2) {
        ary = rb_ary_new2(RARRAY_LEN(obj)*2);
    }
    else {
        ary = rb_ary_new();
    }
    RBASIC_CLEAR_CLASS(ary);
    buf = rb_ary_tmp_new(SORT_BY_BUFSIZE*2);
    rb_ary_store(buf, SORT_BY_BUFSIZE*2-1, Qnil);
    memo = MEMO_NEW(0, 0, 0);
    data = (struct sort_by_data *)&memo->v1;
    RB_OBJ_WRITE(memo, &data->ary, ary);
    RB_OBJ_WRITE(memo, &data->buf, buf);
    data->n = 0;
    rb_block_call(obj, id_each, 0, 0, sort_by_i, (VALUE)memo);
    ary = data->ary;
    buf = data->buf;
    if (data->n) {
        rb_ary_resize(buf, data->n*2);
        rb_ary_concat(ary, buf);
    }
    if (RARRAY_LEN(ary) > 2) {
        RARRAY_PTR_USE(ary, ptr,
                       ruby_qsort(ptr, RARRAY_LEN(ary)/2, 2*sizeof(VALUE),
                                  sort_by_cmp, (void *)ary));
    }
    if (RBASIC(ary)->klass) {
        rb_raise(rb_eRuntimeError, "sort_by reentered");
    }
    for (i=1; i<RARRAY_LEN(ary); i+=2) {
        RARRAY_ASET(ary, i/2, RARRAY_AREF(ary, i));
    }
    rb_ary_resize(ary, RARRAY_LEN(ary)/2);
    RBASIC_SET_CLASS_RAW(ary, rb_cArray);

    return ary;
}
sum(initial_value = 0) → number click to toggle source
sum(initial_value = 0) {|element| ... } → object

With no block given, returns the sum of initial_value and the elements:

(1..100).sum          # => 5050
(1..100).sum(1)       # => 5051
('a'..'d').sum('foo') # => "fooabcd"

Generally, the sum is computed using methods + and each; for performance optimizations, those methods may not be used, and so any redefinition of those methods may not have effect here.

One such optimization: When possible, computes using Gauss’s summation formula n(n+1)/2:

100 * (100 + 1) / 2 # => 5050

With a block given, calls the block with each element; returns the sum of initial_value and the block return values:

(1..4).sum {|i| i*i }                        # => 30
(1..4).sum(100) {|i| i*i }                   # => 130
h = {a: 0, b: 1, c: 2, d: 3, e: 4, f: 5}
h.sum {|key, value| value.odd? ? value : 0 } # => 9
('a'..'f').sum('x') {|c| c < 'd' ? c : '' }  # => "xabc"
static VALUE
enum_sum(int argc, VALUE* argv, VALUE obj)
{
    struct enum_sum_memo memo;
    VALUE beg, end;
    int excl;

    memo.v = (rb_check_arity(argc, 0, 1) == 0) ? LONG2FIX(0) : argv[0];
    memo.block_given = rb_block_given_p();
    memo.n = 0;
    memo.r = Qundef;

    if ((memo.float_value = RB_FLOAT_TYPE_P(memo.v))) {
        memo.f = RFLOAT_VALUE(memo.v);
        memo.c = 0.0;
    }
    else {
        memo.f = 0.0;
        memo.c = 0.0;
    }

    if (RTEST(rb_range_values(obj, &beg, &end, &excl))) {
        if (!memo.block_given && !memo.float_value &&
                (FIXNUM_P(beg) || RB_BIGNUM_TYPE_P(beg)) &&
                (FIXNUM_P(end) || RB_BIGNUM_TYPE_P(end))) {
            return int_range_sum(beg, end, excl, memo.v);
        }
    }

    if (RB_TYPE_P(obj, T_HASH) &&
            rb_method_basic_definition_p(CLASS_OF(obj), id_each))
        hash_sum(obj, &memo);
    else
        rb_block_call(obj, id_each, 0, 0, enum_sum_i, (VALUE)&memo);

    if (memo.float_value) {
        return DBL2NUM(memo.f + memo.c);
    }
    else {
        if (memo.n != 0)
            memo.v = rb_fix_plus(LONG2FIX(memo.n), memo.v);
        if (memo.r != Qundef) {
            memo.v = rb_rational_plus(memo.r, memo.v);
        }
        return memo.v;
    }
}
take(n) → array click to toggle source

For non-negative integer n, returns the first n elements:

r = (1..4)
r.take(2) # => [1, 2]
r.take(0) # => []

h = {foo: 0, bar: 1, baz: 2, bat: 3}
h.take(2) # => [[:foo, 0], [:bar, 1]]
static VALUE
enum_take(VALUE obj, VALUE n)
{
    struct MEMO *memo;
    VALUE result;
    long len = NUM2LONG(n);

    if (len < 0) {
        rb_raise(rb_eArgError, "attempt to take negative size");
    }

    if (len == 0) return rb_ary_new2(0);
    result = rb_ary_new2(len);
    memo = MEMO_NEW(result, 0, len);
    rb_block_call(obj, id_each, 0, 0, take_i, (VALUE)memo);
    return result;
}
take_while {|element| ... } → array click to toggle source
take_while → enumerator

Calls the block with successive elements as long as the block returns a truthy value; returns an array of all elements up to that point:

(1..4).take_while{|i| i < 3 } # => [1, 2]
h = {foo: 0, bar: 1, baz: 2}
h.take_while{|element| key, value = *element; value < 2 }
# => [[:foo, 0], [:bar, 1]]

With no block given, returns an Enumerator.

static VALUE
enum_take_while(VALUE obj)
{
    VALUE ary;

    RETURN_ENUMERATOR(obj, 0, 0);
    ary = rb_ary_new();
    rb_block_call(obj, id_each, 0, 0, take_while_i, ary);
    return ary;
}
tally → new_hash click to toggle source
tally(hash) → hash

Returns a hash containing the counts of equal elements:

  • Each key is an element of self.

  • Each value is the number elements equal to that key.

With no argument:

%w[a b c b c a c b].tally # => {"a"=>2, "b"=>3, "c"=>3}

With a hash argument, that hash is used for the tally (instead of a new hash), and is returned; this may be useful for accumulating tallies across multiple enumerables:

hash = {}
hash = %w[a c d b c a].tally(hash)
hash # => {"a"=>2, "c"=>2, "d"=>1, "b"=>1}
hash = %w[b a z].tally(hash)
hash # => {"a"=>3, "c"=>2, "d"=>1, "b"=>2, "z"=>1}
hash = %w[b a m].tally(hash)
hash # => {"a"=>4, "c"=>2, "d"=>1, "b"=>3, "z"=>1, "m"=> 1}
static VALUE
enum_tally(int argc, VALUE *argv, VALUE obj)
{
    VALUE hash;
    if (rb_check_arity(argc, 0, 1)) {
        hash = rb_convert_type(argv[0], T_HASH, "Hash", "to_hash");
        rb_check_frozen(hash);
    }
    else {
        hash = rb_hash_new();
    }

    return enum_hashify_into(obj, 0, 0, tally_i, hash);
}
to_a → array click to toggle source

Returns an array containing the items in self:

(0..4).to_a # => [0, 1, 2, 3, 4]

Enumerable#entries is an alias for Enumerable#to_a.

static VALUE
enum_to_a(int argc, VALUE *argv, VALUE obj)
{
    VALUE ary = rb_ary_new();

    rb_block_call_kw(obj, id_each, argc, argv, collect_all, ary, RB_PASS_CALLED_KEYWORDS);

    return ary;
}
Also aliased as: entries
to_h → hash click to toggle source
to_h {|element| ... } → hash

When self consists of 2-element arrays, returns a hash each of whose entries is the key-value pair formed from one of those arrays:

[[:foo, 0], [:bar, 1], [:baz, 2]].to_h # => {:foo=>0, :bar=>1, :baz=>2}

When a block is given, the block is called with each element of self; the block should return a 2-element array which becomes a key-value pair in the returned hash:

(0..3).to_h {|i| [i, i ** 2]} # => {0=>0, 1=>1, 2=>4, 3=>9}

Raises an exception if an element of self is not a 2-element array, and a block is not passed.

static VALUE
enum_to_h(int argc, VALUE *argv, VALUE obj)
{
    rb_block_call_func *iter = rb_block_given_p() ? enum_to_h_ii : enum_to_h_i;
    return enum_hashify(obj, argc, argv, iter);
}
to_set(klass = Set, *args, &block) click to toggle source

Makes a set from the enumerable object with given arguments. Needs to require "set" to use this method.

# File lib/set.rb, line 855
def to_set(klass = Set, *args, &block)
  klass.new(self, *args, &block)
end
uniq → array click to toggle source
uniq {|element| ... } → array

With no block, returns a new array containing only unique elements; the array has no two elements e0 and e1 such that e0.eql?(e1):

%w[a b c c b a a b c].uniq       # => ["a", "b", "c"]
[0, 1, 2, 2, 1, 0, 0, 1, 2].uniq # => [0, 1, 2]

With a block, returns a new array containing only for which the block returns a unique value:

a = [0, 1, 2, 3, 4, 5, 5, 4, 3, 2, 1]
a.uniq {|i| i.even? ? i : 0 } # => [0, 2, 4]
a = %w[a b c d e e d c b a a b c d e]
a.uniq {|c| c < 'c' }         # => ["a", "c"]
static VALUE
enum_uniq(VALUE obj)
{
    VALUE hash, ret;
    rb_block_call_func *const func =
        rb_block_given_p() ? uniq_iter : uniq_func;

    hash = rb_obj_hide(rb_hash_new());
    rb_block_call(obj, id_each, 0, 0, func, hash);
    ret = rb_hash_values(hash);
    rb_hash_clear(hash);
    return ret;
}
zip(*other_enums) → array click to toggle source
zip(*other_enums) {|array| ... } → nil

With no block given, returns a new array new_array of size self.size whose elements are arrays. Each nested array new_array[n] is of size other_enums.size+1, and contains:

  • The n-th element of self.

  • The n-th element of each of the other_enums.

If all other_enums and self are the same size, all elements are included in the result, and there is no nil-filling:

a = [:a0, :a1, :a2, :a3]
b = [:b0, :b1, :b2, :b3]
c = [:c0, :c1, :c2, :c3]
d = a.zip(b, c)
d # => [[:a0, :b0, :c0], [:a1, :b1, :c1], [:a2, :b2, :c2], [:a3, :b3, :c3]]

f = {foo: 0, bar: 1, baz: 2}
g = {goo: 3, gar: 4, gaz: 5}
h = {hoo: 6, har: 7, haz: 8}
d = f.zip(g, h)
d # => [
  #      [[:foo, 0], [:goo, 3], [:hoo, 6]],
  #      [[:bar, 1], [:gar, 4], [:har, 7]],
  #      [[:baz, 2], [:gaz, 5], [:haz, 8]]
  #    ]

If any enumerable in other_enums is smaller than self, fills to self.size with nil:

a = [:a0, :a1, :a2, :a3]
b = [:b0, :b1, :b2]
c = [:c0, :c1]
d = a.zip(b, c)
d # => [[:a0, :b0, :c0], [:a1, :b1, :c1], [:a2, :b2, nil], [:a3, nil, nil]]

If any enumerable in other_enums is larger than self, its trailing elements are ignored:

a = [:a0, :a1, :a2, :a3]
b = [:b0, :b1, :b2, :b3, :b4]
c = [:c0, :c1, :c2, :c3, :c4, :c5]
d = a.zip(b, c)
d # => [[:a0, :b0, :c0], [:a1, :b1, :c1], [:a2, :b2, :c2], [:a3, :b3, :c3]]

When a block is given, calls the block with each of the sub-arrays (formed as above); returns nil:

a = [:a0, :a1, :a2, :a3]
b = [:b0, :b1, :b2, :b3]
c = [:c0, :c1, :c2, :c3]
a.zip(b, c) {|sub_array| p sub_array} # => nil

Output:

[:a0, :b0, :c0]
[:a1, :b1, :c1]
[:a2, :b2, :c2]
[:a3, :b3, :c3]
static VALUE
enum_zip(int argc, VALUE *argv, VALUE obj)
{
    int i;
    ID conv;
    struct MEMO *memo;
    VALUE result = Qnil;
    VALUE args = rb_ary_new4(argc, argv);
    int allary = TRUE;

    argv = RARRAY_PTR(args);
    for (i=0; i<argc; i++) {
        VALUE ary = rb_check_array_type(argv[i]);
        if (NIL_P(ary)) {
            allary = FALSE;
            break;
        }
        argv[i] = ary;
    }
    if (!allary) {
        static const VALUE sym_each = STATIC_ID2SYM(id_each);
        CONST_ID(conv, "to_enum");
        for (i=0; i<argc; i++) {
            if (!rb_respond_to(argv[i], id_each)) {
                rb_raise(rb_eTypeError, "wrong argument type %"PRIsVALUE" (must respond to :each)",
                         rb_obj_class(argv[i]));
            }
            argv[i] = rb_funcallv(argv[i], conv, 1, &sym_each);
        }
    }
    if (!rb_block_given_p()) {
        result = rb_ary_new();
    }

    /* TODO: use NODE_DOT2 as memo(v, v, -) */
    memo = MEMO_NEW(result, args, 0);
    rb_block_call(obj, id_each, 0, 0, allary ? zip_ary : zip_i, (VALUE)memo);

    return result;
}