From: Martin DeMello <martindemello@...>
Date: 2005-10-17T16:36:57+09:00
Subject: Re: How to get non-unique elements from an array?

Sam Kong <sam.s.kong@gmail.com> wrote:
> Hello!
> 
> I need to get non-unique elements from an array.
> The best I came up with was using a hash as a counter for each unique
> elements.
> 
> a = [0,1,2,3,4,5,2,3]
> 
> #What I want to get is [2,3] as 2,3 are non-unique elements.

Without counting:

h1 = {}
h2 = {}
a.each {|i| 
  h2[i] = true if h1[i]
  h1[i] = true
}

p h2.keys

martin