From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2006-11-30T03:16:30+09:00
Subject: Re: Array#group_by

On Wed, 2006-11-29 at 22:55 +0900, Gareth Adams wrote:
> class Array
>   # Groups elements of an array based on a user-defined condition
>   # 
>   # Each element from this array is passed to the block, and the returned value
>   # determines the key under which it will be stored in the output hash
>   #
>   # If no block is given then the array indices will be used as the hash keys
>   def group_by
>     hsh = {}
>     self.dup.each_with_index do |element, i|
>       if block_given?
>         key = yield element
>       else
>         key = i
>       end
>       hsh[key] ||= []
>       hsh[key] << element
>     end
>     hsh
>   end
> end

Here's an improved version:

  module Enumerable
    def group_by
      hsh = Hash.new{|hsh, key| hsh[key] = [] }
      if block_given?
        each{|obj| hsh[yield(obj)].push(obj) }
      else
        each_with_index{|obj, i| hsh[i].push(obj) }
      end
      hsh
    end
  end


Cheers,
Daniel Schierbeck