0

假设我有一个多维哈希,并且在其中一个子哈希中我有一个 key=>value 对,我需要通过 key 检索它。我该怎么做?

示例哈希:

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

关键总是:k,我需要得到“针”

我注意到 ruby​​ 1.8 中没有散列的“扁平化”功能,但如果它在那里,我想我会做

h.flatten[:k]

我想我需要为此编写一个递归函数?

谢谢

4

2 回答 2

9

您始终可以为 Hash 编写自己的特定于任务的扩展,它会为您完成繁琐的工作:

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

你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
# => "needle"

h={:k=>"needle"}

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

puts h.recursive_find_by_key(:foo).inspect
# => nil
于 2010-02-10T19:49:46.110 回答
2

如果您只需要获取键值,但不知道键的深度,请使用此代码段

def find_tag_val(hash, tag)
  hash.map do |k, v|
    return v if k.to_sym == tag
    vr = find_tag_val(v, tag) if v.kind_of?(Hash)
    return vr if vr
  end
  nil #othervice
end 

h = {message: { key: 'val'}}
find_tag_val(h, :key) #=> 'val'
于 2013-11-13T07:48:31.517 回答