Ruby便利メソッドまとめ：Array／Hash／Enumerator ref: http://qiita.com/shu_0115/items/5f08a6d58d1acc46fbad

file0.txt

[1, nil, 2, nil, 3, nil].compact
 # => [1, 2, 3]

file1.txt

[1, 2, 3].concat([4, 5, 6])
 # => [1, 2, 3, 4, 5, 6]

file10.txt

['a', 'b', 'c'].sample
 # => "c"

['a', 'b', 'c'].sample(2)
 # => ["b", "a"]

file11.txt

[1, 2, 3, 4, 5].select{ |x| x >= 3 }
 # => [3, 4, 5]

file12.txt

[1, 2, 3, 4, 5].shuffle
 # => [3, 5, 1, 2, 4]

file13.txt

[1, 2, 3, 4, 5].slice(0, 3)
 # => [1, 2, 3]

[1, 2, 3, 4, 5].slice(2..4)
 # => [3, 4, 5]

file14.txt

['e', 'd', 'a', 'b', 'c'].sort
 # => ["a", "b", "c", "d", "e"]

file15.txt

[2, 1, 5, 1, 3, 2, 4, 3].uniq
 # => [2, 1, 5, 3, 4]

file16.txt

{ a: 1, b: 2, c: 3 }.each{ |key, value| puts "#{key} : #{value}" }
----------
a : 1
b : 2
c : 3
----------

file17.txt

{ a: 1, b: 2, c: 3 }.each_key{ |key| p key }
----------
:a
:b
:c
----------

file18.txt

{ a: 1, b: 2, c: 3 }.each_value{ |value| p value }
----------
1
2
3
----------

file19.txt

{ a: 1, b: 2, c: 3 }.has_key?(:b)
 # => true

{ a: 1, b: 2, c: 3 }.has_key?(:z)
 # => false

file2.txt

a = [1, 2, 3]; p a.concat([4, 5, 6]); p a;
----------
[1, 2, 3, 4, 5, 6]
[1, 2, 3, 4, 5, 6]
----------

file20.txt

{ a: 1, b: 2, c: 3 }.has_value?(3)
 # => true

{ a: 1, b: 2, c: 3 }.has_value?(30)
 # => false

file21.txt

{ a: 1, b: 2, c: 3 }.keys
 # => [:a, :b, :c]

file22.txt

{ a: 1, b: 2, c: 3 }.values
 # => [1, 2, 3]

file23.txt

['a', 'b', 'c', 'd', 'e'].each.with_index(1){ |value, index| puts "#{index} : #{value}" }
----------
1 : a
2 : b
3 : c
4 : d
5 : e
----------

file24.txt

[1, 2, 3, 4, 5].all?
 # => true

[1, 2, 3, 4, 5, nil].all?
 # => false

[1, 2, 3, 4, 5].all?{ |x| x < 10 }
 # => true

[1, 2, 3, 4, 5].all?{ |x| x < 5 }
 # => false

file25.txt

[nil, false].none?
 # => true

[1, 2, 3, 4, 5].none?{ |x| x < 0 }
 # => true

file26.txt

[1, 2, 3, 4, 5].any?{ |x| x >= 5 }
 # => true

[1, 2, 3, 4, 5].any?{ |x| x > 5 }
 # => false

file27.txt

[1, 2, 3, 4, 5].one?{ |x| x == 4 }
 # => true

[1, 2, 3, 4, 5].one?{ |x| x <= 4 }
 # => false

file28.txt

[1, 2, 3, 4, 5].count
 # => 5

file29.txt

[1, 2, 3, 4, 5].each_slice(2){ |x| p x }
----------
[1, 2]
[3, 4]
[5]
----------

file3.txt

a = [1, 2, 3]; p (a + [4, 5, 6]); p a;
----------
[1, 2, 3, 4, 5, 6]
[1, 2, 3]
----------

file30.txt

[1, 2, 3, 4, 5].each_cons(2){ |x| p x }
----------
[1, 2]
[2, 3]
[3, 4]
[4, 5]
----------

file31.txt

(1..10).partition{ |x| x % 3 == 0 }
 # => [[3, 6, 9], [1, 2, 4, 5, 7, 8, 10]]

file32.txt

[1, 2, 3, 4, 5].take(3)
 # => [1, 2, 3]

file33.txt

(1..10).group_by{ |x| x % 3 }
 # => {1=>[1, 4, 7, 10], 2=>[2, 5, 8], 0=>[3, 6, 9]}

file34.txt

[1, 2, 3, 4, 5].min
 # => 1

file35.txt

[1, 2, 3, 4, 5].max
 # => 5

file36.txt

[1, 2, 3, 4, 5].minmax
 # => [1, 5]

file4.txt

a = [1, 2, 3, 2, 1]

a.delete(1)
 # => 1

p a
 # => [2, 3, 2]

file5.txt

a = [0, 1, 2, 3, 4, 5]

a.delete_if{ |x| x % 2 == 0 }
 # => [1, 3, 5]

p a
 # => [1, 3, 5]

file6.txt

['a', 'b', 'c'].include?('a')
 # => true

['a', 'b', 'c'].include?('z')
 # => false

file7.txt

['a', 'b', 'c'].index('c')
 # => 2

['a', 'b', 'c'].index('z')
 # => nil

file8.txt

['a', 'b', 'c'].join('-')
 # => "a-b-c"

file9.txt

['a', 'b', 'c'].reverse
 # => ["c", "b", "a"]