unless Hash.instance_methods.include?(:underscore_keys)
  class Hash

    def underscore_keys
      new_hash = {}

      self.each_pair do |key, value|
        if value.respond_to?(:collect!) # Array
          value.collect do |item|
            if item.respond_to?(:each_pair) # Hash item within
              item.underscore_keys
            else
              item
            end
          end
        elsif value.respond_to?(:each_pair) # Hash
          value = value.underscore_keys
        end

        new_key = key.is_a?(String) ? key.underscore : key # only String keys

        new_hash[new_key] = value
      end

      self.replace(new_hash)
    end

  end
end