SameShirtEveryDay.com

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