This post originated from an RSS feed registered with Ruby Buzz by Jeremy Voorhis. Original Post: Ruby and the Arch Feed Title: JVoorhis Feed URL: http://feeds.feedburner.com/jvoorhis Feed Description: JVoorhis is a Rubyist in northeast Ohio. He rambles about Ruby on Rails, development practices, other frameworks such as Django, and on other days he is just full of snark. Latest Ruby Buzz Posts Latest Ruby Buzz Posts by Jeremy Voorhis Latest Posts From JVoorhis

Often when I am faced with what seems a simple programming task but I am missing the requisite tools to make it happen, I think of Paul Graham’s notion of the arch and look for ways to build the language up to my application. A perfect and funny example of this is Enumerable#group_by. Just two days ago, I had written my own implementation of this iterator for a PLANET ARGON development project:

module Enumerable
  def group_by
    self.inject({}) do |h,v|
      i = yield(v)
      h[i] ||= []
      h[i] << v
      h
    end.values
  end
end

It is used like this:

american_cities.group_by { |c| c.state_code }

Oddly enough, today Jason Watkins pointed me to this Rails changeset containing Marcel Molina’s implementation of group_by.

This coincidence, I think, confirms that programming from the bottom-up is both attainable and natural in Ruby language.