Introduction

• 超类： Object
• 包含模块： Enumerable

New

基础

ary = [1, "two", 3.0] #=> [1, "two", 3.0]
ary = Array.new    #=> []
Array.new(3)       #=> [nil, nil, nil]  默认为 nil
Array.new(3, true) #=> [true, true, true]

提高

• new可以跟 block

  Array.new(4) { Hash.new } #=> [{}, {}, {}, {}]
  empty_table = Array.new(3) { Array.new(3) } #=> [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
  

• Hash 转化为 Array

  Array({:a => "a", :b => "b"}) #=> [[:a, "a"], [:b, "b"]]
  {:a => "a", :b => "b"}.to_a  #=> [[:a, "a"], [:b, "b"]]
  

注意点

1. new 的第二个参数，array 将填充同一个 object，==这里有陷阱==

   a = Array.new(2, Hash.new)
   # => [{}, {}]
   
   a[0]['cat'] = 'feline'
   a # => [{"cat"=>"feline"}, {"cat"=>"feline"}]
   
   a[1]['cat'] = 'Felix'
   a # => [{"cat"=>"Felix"}, {"cat"=>"Felix"}]
   
   # 修改第一个 hash，第二个也跟着变，因为是同一个 object
   

2. new 中的 block， array 将填充不同的 object

   a = Array.new(2) { Hash.new }
   a[0]['cat'] = 'feline'
   a # => [{"cat"=>"feline"}, {}]
   

Index

基础

• slice

  arr = [1, 2, 3, 4, 5, 6]
  arr[2]    #=> 3
  arr[100]  #=> nil
  arr[-3]   #=> 4
  

• first，last

  arr.first #=> 1
  arr.last  #=> 6
  

提高

• slice

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

• at，take，drop

  arr.at(0) #=> 1
  arr.take(3) #=> [1, 2, 3]  提取前3个元素
  arr.drop(3) #=> [4, 5, 6]  排除前3个元素
  

• fetch，如果指定的 index 有元素就返回，否则返回指定的信息

  a = [ 11, 22, 33, 44 ]
  a.fetch(1)               #=> 22
  a.fetch(-1)              #=> 44
  a.fetch(4, 'cat')        #=> "cat"  没有元素，返回指定的信息 cat
  a.fetch(100) { |i| puts "#{i} is out of bounds" }  #=> "100 is out of bounds"
  

注意点

1. slice 索引超出范围时需要特别注意，==这里有陷阱==

   a = [ "a", "b", "c", "d", "e" ]
   a[5]                   #=> nil
   a[6, 1]                #=> nil
   a[5, 1]                #=> []
   a[5..10]               #=> []
   

Information

基础

browsers = ['Chrome', 'Firefox', 'Safari', 'Opera', 'IE']
browsers.length #=> 5
browsers.count #=> 5
browsers.size #=> 5

提高

browsers.empty? #=> false
browsers.include?('Konqueror') #=> false

注意点

• count可以跟参数或者 block

  ary = [1, 2, 4, 2]
  ary.count                  #=> 4
  ary.count(2)               #=> 2
  ary.count { |x| x%2 == 0 } #=> 3
  

Add Items

基础

arr = [1, 2, 3, 4]
arr.push(5) #=> [1, 2, 3, 4, 5]
arr << 6    #=> [1, 2, 3, 4, 5, 6]

提高

arr.unshift(0) #=> [0, 1, 2, 3, 4, 5, 6]
arr.insert(3, 'apple')  #=> [0, 1, 2, 'apple', 3, 4, 5, 6]
arr.insert(3, 'orange', 'pear', 'grapefruit')  #=> [0, 1, 2, "orange", "pear", "grapefruit", "apple", 3, 4, 5, 6]

注意点

1. push、unshift和insert 一次可以加入多个元素

   a = [ "b", "c", "d" ]
   a.unshift("a")   #=> ["a", "b", "c", "d"]
   a.unshift(1, 2)  #=> [ 1, 2, "a", "b", "c", "d"]
   

Remove Items

基础

• pop

  arr =  [1, 2, 3, 4, 5, 6]
  arr.pop #=> 6
  arr #=> [1, 2, 3, 4, 5]
  

• shift

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

arr.delete_at(2) #=> 4
arr #=> [2, 3, 5]

提高

• delete

  arr = [1, 2, 2, 3]
  arr.delete(2) #=> 2
  arr #=> [1,3]
  
  # 有多个2，全部被删掉了
  

• compact，删除 nil 项

  arr = ['foo', 0, nil, 'bar', 7, 'baz', nil]
  arr.compact  #=> ['foo', 0, 'bar', 7, 'baz']
  arr          #=> ['foo', 0, nil, 'bar', 7, 'baz', nil]
  
  # arr 的值并没有变化
  

• uniq，合并重复项

  arr = [2, 5, 6, 556, 6, 6, 8, 9, 0, 123, 556]
  arr.uniq #=> [2, 5, 6, 556, 8, 9, 0, 123]
  

注意点

1. delete会将array中所有等于该数值的项都删掉
2. compact!和uniq!可以改变原来 array 的值，==但是返回值有陷阱==

   [ "a", nil, "b", nil, "c" ].compact! #=> [ "a", "b", "c" ]
   [ "a", "b", "c" ].compact!           #=> nil  没有 nil 项会返回 nil
   

   a = [ "a", "a", "b", "b", "c" ]
   a.uniq!   # => ["a", "b", "c"]
   
   b = [ "a", "b", "c" ]
   b.uniq!   # => nil  没有重复项会返回 nil
   

3. uniq!可以跟 block

   c = [["student","sam"], ["student","george"], ["teacher","matz"]]
   c.uniq! { |s| s.first } # => [["student", "sam"], ["teacher", "matz"]]
   

4. slice!也可以用来删除元素

   a = [ "a", "b", "c" ]
   a.slice!(1)     #=> "b"
   a               #=> ["a", "c"]
   a.slice!(-1)    #=> "c"
   a               #=> ["a"]
   a.slice!(100)   #=> nil
   a               #=> ["a"]
   

Iterate Over 遍历

基础

• each

  arr = [1, 2, 3, 4, 5]
  arr.each { |a| print a -= 10, " " }
  # prints: -9 -8 -7 -6 -5
  #=> [1, 2, 3, 4, 5]  原有 array 的值不变
  

• reverse_each，倒序遍历

  words = %w[first second third fourth fifth sixth]
  str = ""
  words.reverse_each { |word| str += "#{word} " }
  p str #=> "sixth fifth fourth third second first "
  

提高

• map

  arr.map { |a| 2*a }   #=> [2, 4, 6, 8, 10]
  arr                   #=> [1, 2, 3, 4, 5]
  

• map!

  arr.map! { |a| a**2 } #=> [1, 4, 9, 16, 25]
  arr                   #=> [1, 4, 9, 16, 25]
  

Select Items

基础