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Personal blog of the one called Alex Gorbatchev, from Toronto, Canada.

Ruby: get full history (all parents) of a hash node

Posted on September 23rd, 2007 by Alex Gorbatchev. In Ruby. 3 comments!

Nested hashes could be used to represent tree structures. Here’s a code to to find a node by key and get all of its parents:

def hash_history(hash, desired_key, &block)
  return false unless Hash === hash

  hash.each_pair do |key, value|
    if key == desired_key or hash_history(value, desired_key, &block)
      yield(key, value)
      return true
    end
  end

  return false
end

hash = {
  :level_1 => {
    :level_2 => {
      :level_3 => {
        :search => 'test'
      }
    }
  }
}

hash_history(hash, :search) { |key, value| puts key }

# prints out...
# search
# level_3
# level_2
# level_1

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3 comments.

Rudolf Olah

September 24th, 4:14 pm #

What’s the advantage of this over using a binary search tree? Is it faster?
Alex Gorbatchev

September 24th, 4:58 pm #

Rudolf,

Not really an advantage over anything, this is just a code snippet illustrating how to get all parent nodes of a tree. I just found it to be a nice combo of recursion and yield.
freno

October 29th, 5:53 am #

For a similar snippet see http://snippets.dzone.com/posts/show/1908 .

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