通过按键名称从ruby中的多维散列提取特定值 [英] extracting specific value from a multidimensional hash in ruby by key name

问题描述

假设我有一个多维散列，并且在其中一个子散列中，我有一个key => value对，我需要通过key来检索。

例子哈希：

  h = {：x => 1，：y => 2，：z => {：a => {：k =>needle}}} 
h = {：k =>针} 
  

键总是：k，我需要获得针

我注意到在ruby 1.8中没有用于哈希的扁平化函数，但如果它在那里，我想我会做$ / b
$ b

  h.flatten [：k] 
  

<我想我需要为它写一个递归函数吗？

谢谢

解决方案

您可以随时编写自己的特定于任务的扩展程序，以便为您做一些肮脏的工作：

  class哈希
 def recursive_find_by_key（key）
＃创建一堆哈希来搜索针头，
＃最初是这个哈希
 stack = [self] 
 
＃只要有更多草垛搜索... 
 while（to_search = stack.pop）
＃...继续搜索这个特定的键... 
 to_search.each do | k，v | 
＃...并返回相应的值，如果找到。 
 return v if（k == key）
 
＃如果这个值可以递归搜索... 
 if（v.respond_to？（：recursive_find_by_key））
＃...将其推送到要搜索的地点列表中。 
堆栈<< v 
结束
结束
结束
结束
结束
  

您可以很简单地使用它：

  h = {：x => 1，：y => ; 2：z => {：a => {：k =>needle}}} 
 
 puts h.recursive_find_by_key（：k）.inspect 
＃= > 针
 
 h = {：k =>needle} 
 
 puts h.recursive_find_by_key（：k）.inspect 
＃=> needle
 
 puts h.recursive_find_by_key（：foo）.inspect 
＃=>无
  

let's say i have a multidimensional hash, and in one of the subhashes i have a key=>value pair which i need to retrieve by key. how can i do it?

example hashes:

h={:x=>1,:y=>2,:z=>{:a=>{:k=>"needle"}}}
h={:k=>"needle"}

key is always :k, and i need to get "needle"

i noticed that there is no "flatten" function for hashes in ruby 1.8, but if it'd be there, i imagine i'd just do

h.flatten[:k]

i imagine i need to write a recursive function for that?

thanks

解决方案

You can always write your own mission-specific extension to Hash which does the dirty work for you:

class Hash
  def recursive_find_by_key(key)
    # Create a stack of hashes to search through for the needle which
    # is initially this hash
    stack = [ self ]

    # So long as there are more haystacks to search...
    while (to_search = stack.pop)
      # ...keep searching for this particular key...
      to_search.each do |k, v|
        # ...and return the corresponding value if it is found.
        return v if (k == key)

        # If this value can be recursively searched...
        if (v.respond_to?(:recursive_find_by_key))
          # ...push that on to the list of places to search.
          stack << v
        end
      end
    end
  end
end

You can use this quite simply:

h={:x=>1,:y=>2,:z=>{:a=>{:k=>"needle"}}}

puts h.recursive_find_by_key(:k).inspect
# => "needle"

h={:k=>"needle"}

puts h.recursive_find_by_key(:k).inspect
# => "needle"

puts h.recursive_find_by_key(:foo).inspect
# => nil

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