nested_only.rb

  def nested_delete_keys(*invalid_keys)
    invalid_keys = invalid_keys.flatten
    keys.each do |key|
      key = key.to_s
      if key.to_s.in?(invalid_keys)
        delete(key)
      elsif self[key].is_a?(Hash)
        self[key].nested_delete_keys(invalid_keys.flatten)
      elsif self[key].is_a?(Array)  && self[key].first.is_a?(Hash)
        self[key].first.nested_delete_keys(*invalid_keys)
      end
    end
    self
  end

  def nested_only(valid_keys_array)
    valid_keys_array = valid_keys_array.flatten
    keys.each do |key|
      if self[key].is_a?(Hash)
        self[key].nested_only(valid_keys_array)
      elsif self[key].is_a?(Array)  && self[key].first.is_a?(Hash)
        self[key].first.nested_only(valid_keys_array)
      elsif !key.in?(valid_keys_array)
        self.delete(key)
      end
    end
    self
  end