From: Adam Shelly <adam.shelly@...>
Date: 2008-09-09T03:15:58+09:00
Subject: Re: Is this a sensible implementation for Array#group_by ?

On Mon, Sep 8, 2008 at 10:04 AM, Max Williams
<toastkid.williams@gmail.com> wrote:
> I was looking for a method to split an array into smaller arrays based
> on some property of the members (set with a code block).  I came up with
> the following and wanted to know what you guys think about a) whether
> it's sensible b) whether it's been done already:
>
> class Array
>  def group_by
>    result_array = []
>    self.each do |element|
>      key = yield element
>      if (found = result_array.assoc(key))
>        found[1] << element
>      else
>        result_array << [key, [element]]
>      end
>    end
>    return result_array.collect{|a| a[1]}
>  end
> end
>

> I'm just after some feedback really.  I'm guessing i just couldn't find
> the  good implementation of it :)

It seems sensible to me, although I'd use a hash instead of a
associative array - it just looks cleaner.  I didn't check the
performance difference though.

class Array
 def group_by
   result={}
   self.each do |element|
     (result[yield(element)]||=[]) << element
-   end
   return result.values
 end
end

I think the Facets library  already has a similar method.
-Adam