class Hash

A Hash is a dictionary-like collection of unique keys and their values. Also called associative arrays, they are similar to Arrays, but where an Array uses integers as its index, a Hash allows you to use any object type.

Hashes enumerate their values in the order that the corresponding keys were inserted.

A Hash can be easily created by using its implicit form:

grades = { "Jane Doe" => 10, "Jim Doe" => 6 }

Hashes allow an alternate syntax form when your keys are always symbols. Instead of

options = { :font_size => 10, :font_family => "Arial" }

You could write it as:

options = { font_size: 10, font_family: "Arial" }

Each named key is a symbol you can access in hash:

options[:font_size]  # => 10

A Hash can also be created through its ::new method:

grades = Hash.new
grades["Dorothy Doe"] = 9

Hashes have a default value that is returned when accessing keys that do not exist in the hash. If no default is set nil is used. You can set the default value by sending it as an argument to ::new:

grades = Hash.new(0)

Or by using the default= method:

grades = {"Timmy Doe" => 8}
grades.default = 0

Accessing a value in a Hash requires using its key:

puts grades["Jane Doe"] # => 10

Common Uses¶ ↑

Hashes are an easy way to represent data structures, such as

books         = {}
books[:matz]  = "The Ruby Language"
books[:black] = "The Well-Grounded Rubyist"

Hashes are also commonly used as a way to have named parameters in functions. Note that no brackets are used below. If a hash is the last argument on a method call, no braces are needed, thus creating a really clean interface:

Person.create(name: "John Doe", age: 27)

def self.create(params)
  @name = params[:name]
  @age  = params[:age]
end

Hash Keys¶ ↑

Two objects refer to the same hash key when their hash value is identical and the two objects are eql? to each other.

A user-defined class may be used as a hash key if the hash and eql? methods are overridden to provide meaningful behavior. By default, separate instances refer to separate hash keys.

A typical implementation of hash is based on the object's data while eql? is usually aliased to the overridden == method:

class Book
  attr_reader :author, :title

  def initialize(author, title)
    @author = author
    @title = title
  end

  def ==(other)
    self.class === other and
      other.author == @author and
      other.title == @title
  end

  alias eql? ==

  def hash
    @author.hash ^ @title.hash # XOR
  end
end

book1 = Book.new 'matz', 'Ruby in a Nutshell'
book2 = Book.new 'matz', 'Ruby in a Nutshell'

reviews = {}

reviews[book1] = 'Great reference!'
reviews[book2] = 'Nice and compact!'

reviews.length #=> 1

Public Class Methods

Hash[ key, value, ... ] → new_hash click to toggle source

Hash[ [ [key, value], ... ] ] → new_hash

Hash[ object ] → new_hash

Creates a new hash populated with the given objects. Equivalent to the literal { key => value, ... }. In the first form, keys and values occur in pairs, so there must be an even number of arguments. The second and third form take a single argument which is either an array of key-value pairs or an object convertible to a hash.

Hash["a", 100, "b", 200]             #=> {"a"=>100, "b"=>200}
Hash[ [ ["a", 100], ["b", 200] ] ]   #=> {"a"=>100, "b"=>200}
Hash["a" => 100, "b" => 200]         #=> {"a"=>100, "b"=>200}

static VALUE
rb_hash_s_create(int argc, VALUE *argv, VALUE klass)
{
    VALUE hash, tmp;
    int i;

    if (argc == 1) {
        tmp = rb_hash_s_try_convert(Qnil, argv[0]);
        if (!NIL_P(tmp)) {
            hash = hash_alloc(klass);
            if (RHASH(tmp)->ntbl) {
                RHASH(hash)->ntbl = st_copy(RHASH(tmp)->ntbl);
            }
            return hash;
        }

        tmp = rb_check_array_type(argv[0]);
        if (!NIL_P(tmp)) {
            long i;

            hash = hash_alloc(klass);
            for (i = 0; i < RARRAY_LEN(tmp); ++i) {
                VALUE e = RARRAY_PTR(tmp)[i];
                VALUE v = rb_check_array_type(e);
                VALUE key, val = Qnil;

                if (NIL_P(v)) {
#if 0 /* refix in the next release */
                    rb_raise(rb_eArgError, "wrong element type %s at %ld (expected array)",
                             rb_builtin_class_name(e), i);

#else
                    rb_warn("wrong element type %s at %ld (expected array)",
                            rb_builtin_class_name(e), i);
                    rb_warn("ignoring wrong elements is deprecated, remove them explicitly");
                    rb_warn("this causes ArgumentError in the next release");
                    continue;
#endif
                }
                switch (RARRAY_LEN(v)) {
                  default:
                    rb_raise(rb_eArgError, "invalid number of elements (%ld for 1..2)",
                             RARRAY_LEN(v));
                  case 2:
                    val = RARRAY_PTR(v)[1];
                  case 1:
                    key = RARRAY_PTR(v)[0];
                    rb_hash_aset(hash, key, val);
                }
            }
            return hash;
        }
    }
    if (argc % 2 != 0) {
        rb_raise(rb_eArgError, "odd number of arguments for Hash");
    }

    hash = hash_alloc(klass);
    for (i=0; i<argc; i+=2) {
        rb_hash_aset(hash, argv[i], argv[i + 1]);
    }

    return hash;
}

new → new_hash click to toggle source

new(obj) → new_hash

new {|hash, key| block } → new_hash

Returns a new, empty hash. If this hash is subsequently accessed by a key that doesn't correspond to a hash entry, the value returned depends on the style of new used to create the hash. In the first form, the access returns nil. If obj is specified, this single object will be used for all default values. If a block is specified, it will be called with the hash object and the key, and should return the default value. It is the block's responsibility to store the value in the hash if required.

h = Hash.new("Go Fish")
h["a"] = 100
h["b"] = 200
h["a"]           #=> 100
h["c"]           #=> "Go Fish"
# The following alters the single default object
h["c"].upcase!   #=> "GO FISH"
h["d"]           #=> "GO FISH"
h.keys           #=> ["a", "b"]

# While this creates a new default object each time
h = Hash.new { |hash, key| hash[key] = "Go Fish: #{key}" }
h["c"]           #=> "Go Fish: c"
h["c"].upcase!   #=> "GO FISH: C"
h["d"]           #=> "Go Fish: d"
h.keys           #=> ["c", "d"]

static VALUE
rb_hash_initialize(int argc, VALUE *argv, VALUE hash)
{
    VALUE ifnone;

    rb_hash_modify(hash);
    if (rb_block_given_p()) {
        rb_check_arity(argc, 0, 0);
        ifnone = rb_block_proc();
        default_proc_arity_check(ifnone);
        RHASH_IFNONE(hash) = ifnone;
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        rb_scan_args(argc, argv, "01", &ifnone);
        RHASH_IFNONE(hash) = ifnone;
    }

    return hash;
}

try_convert(obj) → hash or nil click to toggle source

Try to convert obj into a hash, using #to_hash method. Returns converted hash or nil if obj cannot be converted for any reason.

Hash.try_convert({1=>2})   # => {1=>2}
Hash.try_convert("1=>2")   # => nil

static VALUE
rb_hash_s_try_convert(VALUE dummy, VALUE hash)
{
    return rb_check_hash_type(hash);
}

Public Instance Methods

hsh == other_hash → true or false click to toggle source

Equality—Two hashes are equal if they each contain the same number of keys and if each key-value pair is equal to (according to Object#==) the corresponding elements in the other hash.

h1 = { "a" => 1, "c" => 2 }
h2 = { 7 => 35, "c" => 2, "a" => 1 }
h3 = { "a" => 1, "c" => 2, 7 => 35 }
h4 = { "a" => 1, "d" => 2, "f" => 35 }
h1 == h2   #=> false
h2 == h3   #=> true
h3 == h4   #=> false

static VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, FALSE);
}

hsh[key] → value click to toggle source

Element Reference—Retrieves the value object corresponding to the key object. If not found, returns the default value (see Hash::new for details).

h = { "a" => 100, "b" => 200 }
h["a"]   #=> 100
h["c"]   #=> nil

VALUE
rb_hash_aref(VALUE hash, VALUE key)
{
    st_data_t val;

    if (!RHASH(hash)->ntbl || !st_lookup(RHASH(hash)->ntbl, key, &val)) {
        return hash_default_value(hash, key);
    }
    return (VALUE)val;
}

hsh[key] = value → value click to toggle source

Element Assignment¶ ↑

Associates the value given by value with the key given by key.

h = { "a" => 100, "b" => 200 }
h["a"] = 9
h["c"] = 4
h   #=> {"a"=>9, "b"=>200, "c"=>4}

key should not have its value changed while it is in use as a key (an unfrozen String passed as a key will be duplicated and frozen).

a = "a"
b = "b".freeze
h = { a => 100, b => 200 }
h.key(100).equal? a #=> false
h.key(200).equal? b #=> true

VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    int iter_lev = RHASH_ITER_LEV(hash);
    st_table *tbl = RHASH(hash)->ntbl;

    rb_hash_modify(hash);
    if (!tbl) {
        if (iter_lev > 0) no_new_key();
        tbl = RHASH_TBL(hash);
    }
    if (tbl->type == &identhash || rb_obj_class(key) != rb_cString) {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
    }
    else {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
    }
    return val;
}

assoc(obj) → an_array or nil click to toggle source

Searches through the hash comparing obj with the key using ==. Returns the key-value pair (two elements array) or nil if no match is found. See Array#assoc.

h = {"colors"  => ["red", "blue", "green"],
     "letters" => ["a", "b", "c" ]}
h.assoc("letters")  #=> ["letters", ["a", "b", "c"]]
h.assoc("foo")      #=> nil

VALUE
rb_hash_assoc(VALUE hash, VALUE obj)
{
    VALUE args[2];

    args[0] = obj;
    args[1] = Qnil;
    rb_hash_foreach(hash, assoc_i, (VALUE)args);
    return args[1];
}

clear → hsh click to toggle source

Removes all key-value pairs from hsh.

h = { "a" => 100, "b" => 200 }   #=> {"a"=>100, "b"=>200}
h.clear                          #=> {}

VALUE
rb_hash_clear(VALUE hash)
{
    rb_hash_modify_check(hash);
    if (!RHASH(hash)->ntbl)
        return hash;
    if (RHASH(hash)->ntbl->num_entries > 0) {
        if (RHASH_ITER_LEV(hash) > 0)
            rb_hash_foreach(hash, clear_i, 0);
        else
            st_clear(RHASH(hash)->ntbl);
    }

    return hash;
}

compare_by_identity → hsh click to toggle source

Makes hsh compare its keys by their identity, i.e. it will consider exact same objects as same keys.

h1 = { "a" => 100, "b" => 200, :c => "c" }
h1["a"]        #=> 100
h1.compare_by_identity
h1.compare_by_identity? #=> true
h1["a"]        #=> nil  # different objects.
h1[:c]         #=> "c"  # same symbols are all same.

static VALUE
rb_hash_compare_by_id(VALUE hash)
{
    rb_hash_modify(hash);
    RHASH(hash)->ntbl->type = &identhash;
    rb_hash_rehash(hash);
    return hash;
}

compare_by_identity? → true or false click to toggle source

Returns true if hsh will compare its keys by their identity. Also see Hash#compare_by_identity.

static VALUE
rb_hash_compare_by_id_p(VALUE hash)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (RHASH(hash)->ntbl->type == &identhash) {
        return Qtrue;
    }
    return Qfalse;
}

default(key=nil) → obj click to toggle source

Returns the default value, the value that would be returned by hsh if key did not exist in hsh. See also Hash::new and Hash#default=.

h = Hash.new                            #=> {}
h.default                               #=> nil
h.default(2)                            #=> nil

h = Hash.new("cat")                     #=> {}
h.default                               #=> "cat"
h.default(2)                            #=> "cat"

h = Hash.new {|h,k| h[k] = k.to_i*10}   #=> {}
h.default                               #=> nil
h.default(2)                            #=> 20

static VALUE
rb_hash_default(int argc, VALUE *argv, VALUE hash)
{
    VALUE key, ifnone;

    rb_scan_args(argc, argv, "01", &key);
    ifnone = RHASH_IFNONE(hash);
    if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
        if (argc == 0) return Qnil;
        return rb_funcall(ifnone, id_yield, 2, hash, key);
    }
    return ifnone;
}

default = obj → obj click to toggle source

Sets the default value, the value returned for a key that does not exist in the hash. It is not possible to set the default to a Proc that will be executed on each key lookup.

h = { "a" => 100, "b" => 200 }
h.default = "Go fish"
h["a"]     #=> 100
h["z"]     #=> "Go fish"
# This doesn't do what you might hope...
h.default = proc do |hash, key|
  hash[key] = key + key
end
h[2]       #=> #<Proc:0x401b3948@-:6>
h["cat"]   #=> #<Proc:0x401b3948@-:6>

static VALUE
rb_hash_set_default(VALUE hash, VALUE ifnone)
{
    rb_hash_modify_check(hash);
    RHASH_IFNONE(hash) = ifnone;
    FL_UNSET(hash, HASH_PROC_DEFAULT);
    return ifnone;
}

default_proc → anObject click to toggle source

If Hash::new was invoked with a block, return that block, otherwise return nil.

h = Hash.new {|h,k| h[k] = k*k }   #=> {}
p = h.default_proc                 #=> #<Proc:0x401b3d08@-:1>
a = []                             #=> []
p.call(a, 2)
a                                  #=> [nil, nil, 4]

static VALUE
rb_hash_default_proc(VALUE hash)
{
    if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
        return RHASH_IFNONE(hash);
    }
    return Qnil;
}

default_proc = proc_obj or nil click to toggle source

Sets the default proc to be executed on each failed key lookup.

h.default_proc = proc do |hash, key|
  hash[key] = key + key
end
h[2]       #=> 4
h["cat"]   #=> "catcat"

static VALUE
rb_hash_set_default_proc(VALUE hash, VALUE proc)
{
    VALUE b;

    rb_hash_modify_check(hash);
    if (NIL_P(proc)) {
        FL_UNSET(hash, HASH_PROC_DEFAULT);
        RHASH_IFNONE(hash) = proc;
        return proc;
    }
    b = rb_check_convert_type(proc, T_DATA, "Proc", "to_proc");
    if (NIL_P(b) || !rb_obj_is_proc(b)) {
        rb_raise(rb_eTypeError,
                 "wrong default_proc type %s (expected Proc)",
                 rb_obj_classname(proc));
    }
    proc = b;
    default_proc_arity_check(proc);
    RHASH_IFNONE(hash) = proc;
    FL_SET(hash, HASH_PROC_DEFAULT);
    return proc;
}

delete(key) → value click to toggle source

delete(key) {| key | block } → value

Deletes the key-value pair and returns the value from hsh whose key is equal to key. If the key is not found, returns the default value. If the optional code block is given and the key is not found, pass in the key and return the result of block.

h = { "a" => 100, "b" => 200 }
h.delete("a")                              #=> 100
h.delete("z")                              #=> nil
h.delete("z") { |el| "#{el} not found" }   #=> "z not found"

VALUE
rb_hash_delete(VALUE hash, VALUE key)
{
    VALUE val;

    rb_hash_modify_check(hash);
    val = rb_hash_delete_key(hash, key);
    if (val != Qundef) return val;
    if (rb_block_given_p()) {
        return rb_yield(key);
    }
    return Qnil;
}

delete_if {| key, value | block } → hsh click to toggle source

delete_if → an_enumerator

Deletes every key-value pair from hsh for which block evaluates to true.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.delete_if {|key, value| key >= "b" }   #=> {"a"=>100}

VALUE
rb_hash_delete_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    rb_hash_modify_check(hash);
    if (RHASH(hash)->ntbl)
        rb_hash_foreach(hash, delete_if_i, hash);
    return hash;
}

each {| key, value | block } → hsh click to toggle source

each_pair {| key, value | block } → hsh

each → an_enumerator

each_pair → an_enumerator

Calls block once for each key in hsh, passing the key-value pair as parameters.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each {|key, value| puts "#{key} is #{value}" }

produces:

a is 100
b is 200

static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}

each_key {| key | block } → hsh click to toggle source

each_key → an_enumerator

Calls block once for each key in hsh, passing the key as a parameter.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each_key {|key| puts key }

produces:

a
b

static VALUE
rb_hash_each_key(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    rb_hash_foreach(hash, each_key_i, 0);
    return hash;
}

each_pair {| key, value | block } → hsh click to toggle source

each_pair → an_enumerator

Calls block once for each key in hsh, passing the key-value pair as parameters.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each {|key, value| puts "#{key} is #{value}" }

produces:

a is 100
b is 200

static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}

each_value {| value | block } → hsh click to toggle source

each_value → an_enumerator

Calls block once for each key in hsh, passing the value as a parameter.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each_value {|value| puts value }

produces:

100
200

static VALUE
rb_hash_each_value(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    rb_hash_foreach(hash, each_value_i, 0);
    return hash;
}

empty? → true or false click to toggle source

Returns true if hsh contains no key-value pairs.

{}.empty?   #=> true

static VALUE
rb_hash_empty_p(VALUE hash)
{
    return RHASH_EMPTY_P(hash) ? Qtrue : Qfalse;
}

eql?(other) → true or false click to toggle source

Returns true if hash and other are both hashes with the same content.

static VALUE
rb_hash_eql(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, TRUE);
}

fetch(key [, default] ) → obj click to toggle source

fetch(key) {| key | block } → obj

Returns a value from the hash for the given key. If the key can't be found, there are several options: With no other arguments, it will raise an KeyError exception; if default is given, then that will be returned; if the optional code block is specified, then that will be run and its result returned.

h = { "a" => 100, "b" => 200 }
h.fetch("a")                            #=> 100
h.fetch("z", "go fish")                 #=> "go fish"
h.fetch("z") { |el| "go fish, #{el}"}   #=> "go fish, z"

The following example shows that an exception is raised if the key is not found and a default value is not supplied.

h = { "a" => 100, "b" => 200 }
h.fetch("z")

produces:

prog.rb:2:in `fetch': key not found (KeyError)
 from prog.rb:2

static VALUE
rb_hash_fetch_m(int argc, VALUE *argv, VALUE hash)
{
    VALUE key, if_none;
    st_data_t val;
    long block_given;

    rb_scan_args(argc, argv, "11", &key, &if_none);

    block_given = rb_block_given_p();
    if (block_given && argc == 2) {
        rb_warn("block supersedes default value argument");
    }
    if (!RHASH(hash)->ntbl || !st_lookup(RHASH(hash)->ntbl, key, &val)) {
        if (block_given) return rb_yield(key);
        if (argc == 1) {
            volatile VALUE desc = rb_protect(rb_inspect, key, 0);
            if (NIL_P(desc)) {
                desc = rb_any_to_s(key);
            }
            desc = rb_str_ellipsize(desc, 65);
            rb_raise(rb_eKeyError, "key not found: %s", RSTRING_PTR(desc));
        }
        return if_none;
    }
    return (VALUE)val;
}

flatten → an_array click to toggle source

flatten(level) → an_array

Returns a new array that is a one-dimensional flattening of this hash. That is, for every key or value that is an array, extract its elements into the new array. Unlike Array#flatten, this method does not flatten recursively by default. The optional level argument determines the level of recursion to flatten.

a =  {1=> "one", 2 => [2,"two"], 3 => "three"}
a.flatten    # => [1, "one", 2, [2, "two"], 3, "three"]
a.flatten(2) # => [1, "one", 2, 2, "two", 3, "three"]

static VALUE
rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
{
    VALUE ary, tmp;

    ary = rb_hash_to_a(hash);
    if (argc == 0) {
        argc = 1;
        tmp = INT2FIX(1);
        argv = &tmp;
    }
    rb_funcall2(ary, rb_intern("flatten!"), argc, argv);
    return ary;
}

has_key?(key) → true or false click to toggle source

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

static VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (st_lookup(RHASH(hash)->ntbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}

has_value?(value) → true or false click to toggle source

Returns true if the given value is present for some key in hsh.

h = { "a" => 100, "b" => 200 }
h.has_value?(100)   #=> true
h.has_value?(999)   #=> false

static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}

hash → fixnum click to toggle source

Compute a hash-code for this hash. Two hashes with the same content will have the same hash code (and will compare using eql?).

static VALUE
rb_hash_hash(VALUE hash)
{
    return rb_exec_recursive_outer(recursive_hash, hash, 0);
}

include?(key) → true or false click to toggle source

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

static VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (st_lookup(RHASH(hash)->ntbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}

initialize_copy(p1) click to toggle source

static VALUE
rb_hash_initialize_copy(VALUE hash, VALUE hash2)
{
    st_table *ntbl;

    rb_hash_modify_check(hash);
    hash2 = to_hash(hash2);

    Check_Type(hash2, T_HASH);

    if (hash == hash2) return hash;

    ntbl = RHASH(hash)->ntbl;
    if (RHASH(hash2)->ntbl) {
        if (ntbl) st_free_table(ntbl);
        RHASH(hash)->ntbl = st_copy(RHASH(hash2)->ntbl);
        if (RHASH(hash)->ntbl->num_entries)
            rb_hash_rehash(hash);
    }
    else if (ntbl) {
        st_clear(ntbl);
    }

    if (FL_TEST(hash2, HASH_PROC_DEFAULT)) {
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        FL_UNSET(hash, HASH_PROC_DEFAULT);
    }
    RHASH_IFNONE(hash) = RHASH_IFNONE(hash2);

    return hash;
}

to_s → string click to toggle source

inspect → string

Return the contents of this hash as a string.

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
h.to_s   #=> "{\"c\"=>300, \"a\"=>100, \"d\"=>400}"

static VALUE
rb_hash_inspect(VALUE hash)
{
    if (RHASH_EMPTY_P(hash))
        return rb_usascii_str_new2("{}");
    return rb_exec_recursive(inspect_hash, hash, 0);
}

Also aliased as: to_s

invert → new_hash click to toggle source

Returns a new hash created by using hsh's values as keys, and the keys as values.

h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
h.invert   #=> {0=>"a", 100=>"m", 200=>"d", 300=>"y"}

static VALUE
rb_hash_invert(VALUE hash)
{
    VALUE h = rb_hash_new();

    rb_hash_foreach(hash, rb_hash_invert_i, h);
    return h;
}

keep_if {| key, value | block } → hsh click to toggle source

keep_if → an_enumerator

Deletes every key-value pair from hsh for which block evaluates to false.

If no block is given, an enumerator is returned instead.

VALUE
rb_hash_keep_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    rb_hash_modify_check(hash);
    if (RHASH(hash)->ntbl)
        rb_hash_foreach(hash, keep_if_i, hash);
    return hash;
}

key(value) → key click to toggle source

Returns the key of an occurrence of a given value. If the value is not found, returns nil.

h = { "a" => 100, "b" => 200, "c" => 300, "d" => 300 }
h.key(200)   #=> "b"
h.key(300)   #=> "c"
h.key(999)   #=> nil

static VALUE
rb_hash_key(VALUE hash, VALUE value)
{
    VALUE args[2];

    args[0] = value;
    args[1] = Qnil;

    rb_hash_foreach(hash, key_i, (VALUE)args);

    return args[1];
}

key?(key) → true or false click to toggle source

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

static VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (st_lookup(RHASH(hash)->ntbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}

keys → array click to toggle source

Returns a new array populated with the keys from this hash. See also Hash#values.

h = { "a" => 100, "b" => 200, "c" => 300, "d" => 400 }
h.keys   #=> ["a", "b", "c", "d"]

static VALUE
rb_hash_keys(VALUE hash)
{
    VALUE ary;

    ary = rb_ary_new();
    rb_hash_foreach(hash, keys_i, ary);

    return ary;
}

length → fixnum click to toggle source

Returns the number of key-value pairs in the hash.

h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
h.length        #=> 4
h.delete("a")   #=> 200
h.length        #=> 3

static VALUE
rb_hash_size(VALUE hash)
{
    if (!RHASH(hash)->ntbl)
        return INT2FIX(0);
    return INT2FIX(RHASH(hash)->ntbl->num_entries);
}

member?(key) → true or false click to toggle source

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

static VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (!RHASH(hash)->ntbl)
        return Qfalse;
    if (st_lookup(RHASH(hash)->ntbl, key, 0)) {
        return Qtrue;
    }
    return Qfalse;
}

merge(other_hash) → new_hash click to toggle source

merge(other_hash){|key, oldval, newval| block} → new_hash

Returns a new hash containing the contents of other_hash and the contents of hsh. If no block is specified, the value for entries with duplicate keys will be that of other_hash. Otherwise the value for each duplicate key is determined by calling the block with the key, its value in hsh and its value in other_hash.

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.merge(h2)   #=> {"a"=>100, "b"=>254, "c"=>300}
h1.merge(h2){|key, oldval, newval| newval - oldval}
               #=> {"a"=>100, "b"=>54,  "c"=>300}
h1             #=> {"a"=>100, "b"=>200}

static VALUE
rb_hash_merge(VALUE hash1, VALUE hash2)
{
    return rb_hash_update(rb_obj_dup(hash1), hash2);
}

merge!(other_hash) → hsh click to toggle source

merge!(other_hash){|key, oldval, newval| block} → hsh

Adds the contents of other_hash to hsh. If no block is specified, entries with duplicate keys are overwritten with the values from other_hash, otherwise the value of each duplicate key is determined by calling the block with the key, its value in hsh and its value in other_hash.

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.merge!(h2)   #=> {"a"=>100, "b"=>254, "c"=>300}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.merge!(h2) { |key, v1, v2| v1 }
                #=> {"a"=>100, "b"=>200, "c"=>300}

static VALUE
rb_hash_update(VALUE hash1, VALUE hash2)
{
    rb_hash_modify(hash1);
    hash2 = to_hash(hash2);
    if (rb_block_given_p()) {
        rb_hash_foreach(hash2, rb_hash_update_block_i, hash1);
    }
    else {
        rb_hash_foreach(hash2, rb_hash_update_i, hash1);
    }
    return hash1;
}

pretty_print(q) click to toggle source

# File lib/pp.rb, line 342
def pretty_print(q)
  q.pp_hash self
end

pretty_print_cycle(q) click to toggle source

# File lib/pp.rb, line 346
def pretty_print_cycle(q)
  q.text(empty? ? '{}' : '{...}')
end

rassoc(obj) → an_array or nil click to toggle source

Searches through the hash comparing obj with the value using ==. Returns the first key-value pair (two-element array) that matches. See also Array#rassoc.

a = {1=> "one", 2 => "two", 3 => "three", "ii" => "two"}
a.rassoc("two")    #=> [2, "two"]
a.rassoc("four")   #=> nil

VALUE
rb_hash_rassoc(VALUE hash, VALUE obj)
{
    VALUE args[2];

    args[0] = obj;
    args[1] = Qnil;
    rb_hash_foreach(hash, rassoc_i, (VALUE)args);
    return args[1];
}

rehash → hsh click to toggle source

Rebuilds the hash based on the current hash values for each key. If values of key objects have changed since they were inserted, this method will reindex hsh. If Hash#rehash is called while an iterator is traversing the hash, an RuntimeError will be raised in the iterator.

a = [ "a", "b" ]
c = [ "c", "d" ]
h = { a => 100, c => 300 }
h[a]       #=> 100
a[0] = "z"
h[a]       #=> nil
h.rehash   #=> {["z", "b"]=>100, ["c", "d"]=>300}
h[a]       #=> 100

static VALUE
rb_hash_rehash(VALUE hash)
{
    VALUE tmp;
    st_table *tbl;

    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "rehash during iteration");
    }
    rb_hash_modify_check(hash);
    if (!RHASH(hash)->ntbl)
        return hash;
    tmp = hash_alloc(0);
    tbl = st_init_table_with_size(RHASH(hash)->ntbl->type, RHASH(hash)->ntbl->num_entries);
    RHASH(tmp)->ntbl = tbl;

    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tbl);
    st_free_table(RHASH(hash)->ntbl);
    RHASH(hash)->ntbl = tbl;
    RHASH(tmp)->ntbl = 0;

    return hash;
}

reject {| key, value | block } → a_hash click to toggle source

reject → an_enumerator

Same as Hash#delete_if, but works on (and returns) a copy of the hsh. Equivalent to hsh.dup.delete_if.

static VALUE
rb_hash_reject(VALUE hash)
{
    return rb_hash_delete_if(rb_obj_dup(hash));
}

reject! {| key, value | block } → hsh or nil click to toggle source

reject! → an_enumerator

Equivalent to Hash#delete_if, but returns nil if no changes were made.

VALUE
rb_hash_reject_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    rb_hash_modify(hash);
    if (!RHASH(hash)->ntbl)
        return Qnil;
    n = RHASH(hash)->ntbl->num_entries;
    rb_hash_foreach(hash, delete_if_i, hash);
    if (n == RHASH(hash)->ntbl->num_entries) return Qnil;
    return hash;
}

replace(other_hash) → hsh click to toggle source

Replaces the contents of hsh with the contents of other_hash.

h = { "a" => 100, "b" => 200 }
h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}

static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    rb_hash_modify_check(hash);
    hash2 = to_hash(hash2);
    if (hash == hash2) return hash;
    rb_hash_clear(hash);
    if (RHASH(hash2)->ntbl) {
        rb_hash_tbl(hash);
        RHASH(hash)->ntbl->type = RHASH(hash2)->ntbl->type;
    }
    rb_hash_foreach(hash2, replace_i, hash);
    RHASH_IFNONE(hash) = RHASH_IFNONE(hash2);
    if (FL_TEST(hash2, HASH_PROC_DEFAULT)) {
        FL_SET(hash, HASH_PROC_DEFAULT);
    }
    else {
        FL_UNSET(hash, HASH_PROC_DEFAULT);
    }

    return hash;
}

select {|key, value| block} → a_hash click to toggle source

select → an_enumerator

Returns a new hash consisting of entries for which the block returns true.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.select {|k,v| k > "a"}  #=> {"b" => 200, "c" => 300}
h.select {|k,v| v < 200}  #=> {"a" => 100}

VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    result = rb_hash_new();
    rb_hash_foreach(hash, select_i, result);
    return result;
}

select! {| key, value | block } → hsh or nil click to toggle source

select! → an_enumerator

Equivalent to Hash#keep_if, but returns nil if no changes were made.

VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, rb_hash_size);
    rb_hash_modify_check(hash);
    if (!RHASH(hash)->ntbl)
        return Qnil;
    n = RHASH(hash)->ntbl->num_entries;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH(hash)->ntbl->num_entries) return Qnil;
    return hash;
}

shift → anArray or obj click to toggle source

Removes a key-value pair from hsh and returns it as the two-item array [ key, value ], or the hash's default value if the hash is empty.

h = { 1 => "a", 2 => "b", 3 => "c" }
h.shift   #=> [1, "a"]
h         #=> {2=>"b", 3=>"c"}

static VALUE
rb_hash_shift(VALUE hash)
{
    struct shift_var var;

    rb_hash_modify_check(hash);
    if (RHASH(hash)->ntbl) {
        var.key = Qundef;
        rb_hash_foreach(hash, RHASH_ITER_LEV(hash) > 0 ? shift_i_safe : shift_i,
                        (VALUE)&var);

        if (var.key != Qundef) {
            if (RHASH_ITER_LEV(hash) > 0) {
                rb_hash_delete_key(hash, var.key);
            }
            return rb_assoc_new(var.key, var.val);
        }
    }
    return hash_default_value(hash, Qnil);
}

size → fixnum click to toggle source

Returns the number of key-value pairs in the hash.

h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
h.length        #=> 4
h.delete("a")   #=> 200
h.length        #=> 3

static VALUE
rb_hash_size(VALUE hash)
{
    if (!RHASH(hash)->ntbl)
        return INT2FIX(0);
    return INT2FIX(RHASH(hash)->ntbl->num_entries);
}

store(key, value) → value click to toggle source

Element Assignment¶ ↑

Associates the value given by value with the key given by key.

h = { "a" => 100, "b" => 200 }
h["a"] = 9
h["c"] = 4
h   #=> {"a"=>9, "b"=>200, "c"=>4}

key should not have its value changed while it is in use as a key (an unfrozen String passed as a key will be duplicated and frozen).

a = "a"
b = "b".freeze
h = { a => 100, b => 200 }
h.key(100).equal? a #=> false
h.key(200).equal? b #=> true

VALUE
rb_hash_aset(VALUE hash, VALUE key, VALUE val)
{
    int iter_lev = RHASH_ITER_LEV(hash);
    st_table *tbl = RHASH(hash)->ntbl;

    rb_hash_modify(hash);
    if (!tbl) {
        if (iter_lev > 0) no_new_key();
        tbl = RHASH_TBL(hash);
    }
    if (tbl->type == &identhash || rb_obj_class(key) != rb_cString) {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset, val);
    }
    else {
        RHASH_UPDATE_ITER(hash, iter_lev, key, hash_aset_str, val);
    }
    return val;
}

to_a → array click to toggle source

Converts hsh to a nested array of [ key, value ] arrays.

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
h.to_a   #=> [["c", 300], ["a", 100], ["d", 400]]

static VALUE
rb_hash_to_a(VALUE hash)
{
    VALUE ary;

    ary = rb_ary_new();
    rb_hash_foreach(hash, to_a_i, ary);
    OBJ_INFECT(ary, hash);

    return ary;
}

to_h → hsh or new_hash click to toggle source

Returns self. If called on a subclass of Hash, converts the receiver to a Hash object.

static VALUE
rb_hash_to_h(VALUE hash)
{
    if (rb_obj_class(hash) != rb_cHash) {
        VALUE ret = rb_hash_new();
        if (!RHASH_EMPTY_P(hash))
            RHASH(ret)->ntbl = st_copy(RHASH(hash)->ntbl);
        if (FL_TEST(hash, HASH_PROC_DEFAULT)) {
            FL_SET(ret, HASH_PROC_DEFAULT);
        }
        RHASH_IFNONE(ret) = RHASH_IFNONE(hash);
        return ret;
    }
    return hash;
}

to_hash → hsh click to toggle source

Returns self.

static VALUE
rb_hash_to_hash(VALUE hash)
{
    return hash;
}

to_s()

Alias for: inspect

update(other_hash) → hsh click to toggle source

update(other_hash){|key, oldval, newval| block} → hsh

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.merge!(h2)   #=> {"a"=>100, "b"=>254, "c"=>300}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 254, "c" => 300 }
h1.merge!(h2) { |key, v1, v2| v1 }
                #=> {"a"=>100, "b"=>200, "c"=>300}

static VALUE
rb_hash_update(VALUE hash1, VALUE hash2)
{
    rb_hash_modify(hash1);
    hash2 = to_hash(hash2);
    if (rb_block_given_p()) {
        rb_hash_foreach(hash2, rb_hash_update_block_i, hash1);
    }
    else {
        rb_hash_foreach(hash2, rb_hash_update_i, hash1);
    }
    return hash1;
}

value?(value) → true or false click to toggle source

Returns true if the given value is present for some key in hsh.

h = { "a" => 100, "b" => 200 }
h.has_value?(100)   #=> true
h.has_value?(999)   #=> false

static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}

values → array click to toggle source

Returns a new array populated with the values from hsh. See also Hash#keys.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.values   #=> [100, 200, 300]

static VALUE
rb_hash_values(VALUE hash)
{
    VALUE ary;

    ary = rb_ary_new();
    rb_hash_foreach(hash, values_i, ary);

    return ary;
}

values_at(key, ...) → array click to toggle source

Return an array containing the values associated with the given keys. Also see Hash.select.

h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }
h.values_at("cow", "cat")  #=> ["bovine", "feline"]

VALUE
rb_hash_values_at(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;

    for (i=0; i<argc; i++) {
        rb_ary_push(result, rb_hash_aref(hash, argv[i]));
    }
    return result;
}