code2.rb

require 'json'

file = File.read('./event.json')
event = JSON.parse(file)
keys = event['windows']['perfmon']['metrics']
hash=keys.map { |key, value| 
	key.split('_').reverse.reduce(value) { 
		|key_value, next_key| {
			next_key => key_value
		} 
	} 
}

class Hash

  def deep_merge(other_hash, &block)
    dup.deep_merge!(other_hash, &block)
  end

  # Same as +deep_merge+, but modifies +self+.
  def deep_merge!(other_hash, &block)
    merge!(other_hash) do |key, this_val, other_val|
      if this_val.is_a?(Hash) && other_val.is_a?(Hash)
        this_val.deep_merge(other_val, &block)
      elsif block_given?
        block.call(key, this_val, other_val)
      else
        other_val
      end
    end
  end
end

class Foo
  #def values = hash.to_json
end
val = {}
Foo.new.values.each do |x|
  val = val.deep_merge(x)
end