From: William James <w_a_x_man@...>
Date: 2007-08-20T04:34:57+09:00
Subject: Re: Detecting duplicates in an array, anything in the standard library ?

On Aug 19, 5:38 am, Thibaut Barr�re <thibaut.barr...@gmail.com> wrote:
> Hi!
>
> Just wondering if there is something simple already built in the std
> library to remove duplicates from an array (or an enumerable). I've
> seen and used various approaches, like:
>
> module Enumerable
>   def dups
>     inject({}) {|h,v| h[v]=h[v].to_i+1; h}.reject{|k,v| v==1}.keys
>   end
> end
>
> which will give:
>
> > %w(a b c c).dups
>
> => ["c"]
>
> Anything more elegant ?
>
> cheers
>
> Thibaut

Here's a modification of a technique used by
Simon Kroger:

class Array
  def dups
    values_at( * (0...size).to_a - uniq.map{|x| index(x)} )
  end
end
    ==>nil

%w(a b a c c d).dups
    ==>["a", "c"]