From: Jimmy Kofler <koflerjim@...>
Date: 2009-01-15T20:18:54+09:00
Subject: Re: Returning a duplicate from an Array

> Pierre Pat wrote:
> I'd do like this:
> a.select{|x| a.index(x) != a.rindex(x)}.uniq
> 
> Now, I wouldn't know which one is more efficient, but coding wise, I 
> like that way :-)

Here's yet another take on it:

class Array
   def dups
      uniq.select{ |e| (self-[e]).size < self.size - 1 }
   end
end

p [ 1, 1, 2, 2, 3, 3, 4, 5 ].dups   #=> [1, 2, 3]

see: http://snippets.dzone.com/posts/show/4148

Cheers,

j.k.
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