判断列表

all? any? none? one?如果有代码块，则以代码块的返回值判断；如果没有代码块，则用自身元素判断。

all? The method returns true if the block never returns false or nil

any? The method returns true if the block ever returns a value other than false or nil

none? The method returns true if the block never returns true for all elements

one? The method returns true if the block returns true exactly once

[1, 2, 3, 4].all? { |x| x<3 }   # false
[1, 2, 3, 4].any? { |x| x<3 }   # true
[1, 2, 3, 4].none? { |x| x<1 }  # true
[1, 2, 3, 4].one? { |x| x<1 }  # false

include? 和 member? 是否包含某个元素

筛选列表中的元素

select 和 find_all 选择代码块中为 true 的元素

[1, 2, 3, 4].select { |x| x < 3 }   # [1, 2]

reject 选择代码块中为 false 的元素

[1, 2, 3, 4].reject { |x| x < 3 }   # [3, 4]

detect 和 find Returns the first for which block is not false

[1, 2, 3, 4].detect{|x| x >2}    # 3
[1, 2, 3, 4].find(Proc.new { 0 }) { |x| x < 1 }   # 0

对列表中的元素进行操作

collect 和 map Returns a new array with the results of running block once for every element in enum.

[1, 2, 3, 4].map(&:to_s)    # ["1", "2", "3", "4"]

inject 和 reduce

(5..10).reduce(:+)                            # 45
(5..10).inject {|sum, n| sum + n }            # 45
(5..10).reduce(0, :+)                         # 45
(5..10).inject{|max, x| max > x ? max : x }   # 10