通过按键名称从ruby中的多维散列提取特定值

通过按键名称从ruby中的多维散列提取特定值

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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] 





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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08-18 13:21