From: "pauldacus@..." <pauldacus@...>
Date: 2005-10-18T04:11:58+09:00
Subject: Re: How to get non-unique elements from an array?

That '?!' zero width lookahead regex is nice, Simon.

A workable alternative, with nary a block or hash counter to offend the
eye:

a.sort.join(' ').to_s.scan(/(\d+)\s(\1)+/).flatten.uniq

This works for all numbers, not just single digits.  Returns a string,
which you will 'to_i' in an iterator.  Replace the \d with \w for
something to find dup strings... I think.