gistfile1.rb

def some_method      
  fields_of_interest = %w{time date number_of_guests}

  modified = self.changes.keep_if do |key, value| 
    keep_or_not = false
    fields_of_interest.each { |field| keep_or_not = true if field == key }
    keep_or_not
  end

  modified.do_something
end