From: "Peña, Botp" <botp@...>
Date: 2007-08-21T17:22:26+09:00
Subject: Re: Detecting duplicates in an array, anything in the standa

From: Peña, Botp [mailto:botp@delmonte-phil.com] 
# irb(main):015:0> a.select{|e| (a-[e]).size < a.size - 1}.uniq
# => [1, 2]

oops,

irb(main):014:0> a
=> [1, 1, 2, 2, 2, 4, 3]
irb(main):015:0> a.uniq.select{|e| (a-[e]).size < a.size - 1}
=> [1, 2]