From: "Peña, Botp" <botp@...>
Date: 2008-05-23T11:21:15+09:00
Subject: Re: Is rdoc (http://www.ruby-doc.org/core/) complete?

From: Victor Reyes [mailto:victor.reyes@gmail.com] 
#thank you for the code snippet.

also try ruby1.8.7 or ruby1.9

036:0> a
=> [1, 2, 3, 4, 3, 2, 1, 2, 3, 4, 5, 6, 5, 4, 3, 4, 5, 6, 7, 8, 7, 8, 9]

037:0> a.group_by{|k| k }.inject({}){|h,(k,v)| h[k] = v.size; h }
=> {1=>2, 2=>3, 3=>4, 4=>4, 5=>3, 6=>2, 7=>2, 8=>2, 9=>1}