在密钥中交换密钥和值 [英] Swapping keys and values in a hash

问题描述

在Ruby中，如何交换Hash上的键和值？

假设我有以下哈希：

  {：a =>：one，：b =>：two，：c =>：three} 
  
 
 
 
我想转换成： 
 
 
  { ：one =>：a，：two =>：b，：three =>：c} 
使用地图似乎相当乏味。是否有更简单的解决方案？
解决方案
 Ruby有一个散列帮助方法，可以让你像对待散列那样对待散列。  
 
 
  {a：1，b：2，c：3} .key（1）
 => ：a 
  
如果您想保留倒排散列，那么Hash#invert 适用于大多数情况。
  {a：1，b：2，c：3} .invert 
 => {1 => a，2 => b，3 => c} 
  
  BUT ...  
 
 
 
如果您有重复的值， invert 将放弃所有但你最后的价值。同样，键只会返回第一个匹配项。  
 
 
  {a：1，b：2，c：2} .key（2）
 => ：b 
 
 {a：1，b：2，c：2} .invert 
 => {1 =>：a，2 =>：c} 
  
是独一无二的，你可以使用 Hash＃invert 如果不是，那么你可以将所有的值保存为一个数组，如下所示：
  class Hash 
＃like invert but no lossy 
＃{one=> 1，two=> 2，1= > 1，2=> 2} .inverse => {1 => [one，1]，2 => [two，2]} 
 def safe_invert 
 each_with_object（{}）do |（key，value ），出于| 
出[值] || = [] 
出[值]<< key 
 end 
 end 
 end 
  
注意：测试现在此处。  
 
 
或者简而言之...  
 
 
  class Hash 
 def safe_invert 
 self.each_with_object（{}）{|（k，v），o |（o [v] || = []）<<< k} 
 end 
结束
  
 
In Ruby, how do I swap keys and values on a Hash?


Let's say I have the following Hash:
{:a=>:one, :b=>:two, :c=>:three}
That I want to transform into:
{:one=>:a, :two=>:b, :three=>:c}
Using a map seems rather tedious. Is there a shorter solution?
解决方案
Ruby has a helper method for hash that lets you treat a hash as if it was inverted. 
{a: 1, b: 2, c: 3}.key(1)
=> :a
If you want to keep the inverted hash, then Hash#invert should work for most situations.
{a: 1, b: 2, c: 3}.invert
=> {1=>:a, 2=>:b, 3=>:c}
BUT...

If you have duplicate values, invert will discarding all but the last of your values. Likewise key will only return the first match. 
{a: 1, b: 2, c: 2}.key(2)
=> :b

{a: 1, b: 2, c: 2}.invert
=> {1=>:a, 2=>:c}
So.. if your values are unique you can use Hash#invert if not, then you can keep all the values as an array, like this:
class Hash
  # like invert but not lossy
  # {"one"=>1,"two"=>2, "1"=>1, "2"=>2}.inverse => {1=>["one", "1"], 2=>["two", "2"]} 
  def safe_invert
    each_with_object({}) do |(key,value),out| 
      out[value] ||= []
      out[value] << key
    end
  end
end
Note: This code with tests is now here. 

Or in short...
class Hash
  def safe_invert
    self.each_with_object({}){|(k,v),o|(o[v]||=[])<<k}
  end
end


                        
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