# instance method Enumerable#max_by

`max_by -> Enumerator`[permalink][rdoc]
`max_by(n) -> Enumerator`
`max_by {|item| ... } -> object | nil`
`max_by(n) {|item| ... } -> Array`

Enumerable#maxEnumerable#max_by の 違いは Enumerable#sortEnumerable#sort_by の違いと同じです。

ブロックを省略した場合は Enumerator を返します。

[PARAM] n:

```a = %w(albatross dog horse)
a.max_by                    # => #<Enumerator: ["albatross", "dog", "horse"]:max_by>
a.max_by { |x| x.length }   # => "albatross"
```

```a = %w[albatross dog horse]
a.max_by(2)                 # => #<Enumerator: ["albatross", "dog", "horse"]:max_by(2)>
a.max_by(2) {|x| x.length } # => ["albatross", "horse"]
```

```module Enumerable
# weighted random sampling.
#
# Pavlos S. Efraimidis, Paul G. Spirakis
# Weighted random sampling with a reservoir
# Information Processing Letters
# Volume 97, Issue 5 (16 March 2006)
def wsample(n)
self.max_by(n) {|v| rand ** (1.0/yield(v)) }
end
end
e = (-20..20).to_a*10000
a = e.wsample(20000) {|x|
Math.exp(-(x/5.0)**2) # normal distribution
}
# a is 20000 samples from e.
p a.length #=> 20000
h = a.group_by {|x| x }
-10.upto(10) {|x| puts "*" * (h[x].length/30.0).to_i if h[x] }
#=> *
#   ***
#   ******
#   ***********
#   ******************
#   *****************************
#   *****************************************
#   ****************************************************
#   ***************************************************************
#   ********************************************************************
#   ***********************************************************************
#   ***********************************************************************
#   **************************************************************
#   ****************************************************
#   ***************************************
#   ***************************
#   ******************
#   ***********
#   *******
#   ***
#   *
```

[SEE_ALSO] Enumerable#sort_by