Enumerable模块的常用方法

enum.collect {| obj | block} => array
enum.map {| obj | block} => array

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

(1..4).collect {|i| i*i }   #=> [1, 4, 9, 16]
(1..4).collect { "cat"  }   #=> ["cat", "cat", "cat", "cat"]

enum.detect(ifnone = nil) {| obj | block } => obj or nil
enum.find(ifnone = nil) {| obj | block } => obj or nil

Passes each entry in enum to block. Returns the first for which block is not false. If no object matches, calls ifnone and returns its result when it is specified, or returns nil.

(1..10).detect  {|i| i % 5 == 0 and i % 7 == 0 }   #=> nil
(1..100).detect {|i| i % 5 == 0 and i % 7 == 0 }   #=> 35

enum.inject(initial) {| memo, obj | block } => obj
enum.inject {| memo, obj | block } => obj

Combines the elements of enum by applying the block to an accumulator value (memo) and each element in turn. At each step, memo is set to the value returned by the block. The first form lets you supply an initial value for memo. The second form uses the first element of the collection as a the initial value (and skips that element while iterating).

# Sum some numbers
(5..10).inject {|sum, n| sum + n }              #=> 45
# Multiply some numbers
(5..10).inject(1) {|product, n| product * n }   #=> 151200

# find the longest word
longest = %w{ cat sheep bear }.inject do |memo,word|
   memo.length > word.length ? memo : word
end
longest                                         #=> "sheep"

# find the length of the longest word
longest = %w{ cat sheep bear }.inject(0) do |memo,word|
   memo >= word.length ? memo : word.length
end
longest                                         #=> 5

enum.find_all {| obj | block } => array
enum.select {| obj | block } => array

Returns an array containing all elements of enum for which block is not false.

(1..10).find_all {|i|  i % 3 == 0 }   #=> [3, 6, 9]

enum.reject {| obj | block } => array

Returns an array for all elements of enum for which block is false.

(1..10).reject {|i|  i % 3 == 0 }   #=> [1, 2, 4, 5, 7, 8, 10]