From: Ryan Davis <ryand-ruby@...>
Date: 2007-08-21T19:02:44+09:00
Subject: Re: Detecting duplicates in an array, anything in the standa


On Aug 21, 2007, at 01:59 , Pe�a, Botp wrote:

> From: Robert Klemme [mailto:shortcutter@googlemail.com]
> # irb(main):002:0> a.uniq.select{|e| (a-[e]).size < a.size - 1}
>
> compare also,
>
> irb(main):056:0> b=a.dup
> => [1, 1, 2, 2, 2, 4, 3]
> irb(main):057:0> b.uniq.select{|e| (b.reject!{|f| f == e}).size > 1}
> => [1, 2]

I came up with something vaguely similar:

class Array
   def dupes
     a = self.dup
     self.partition { |o| a.delete(o) }.last
   end
end

 >> [1,2,2,3,4,4].dupes
=> [2, 4]