From: Sam Duncan <sduncan@...>
Date: 2012-04-20T07:58:26+09:00
Subject: Re: finding duplicates in an array and its index number

On 20/04/12 09:53, newto ruby wrote:
> Hi,
>
> I have following array and I am trying to find if there are duplicates
> in the array. I also want to find out their index.
>
> e.g.
>
> a=[1,2,3,1,3]
>
> Here 1 is a duplicate which comes twice and its index is 0 and 3 in the
> array.
>
> Any suggestions?
>
> Thanks
>
How about;

1.9.3p125 :001 > foo = [1,2,3,1,3]
  => [1, 2, 3, 1, 3]
1.9.3p125 :002 > dup_indices = Hash.new {|h,k| h[k]=[]}
  => {}
1.9.3p125 :003 > foo.each_index {|i| dup_indices[foo[i]] << i unless 1 
== foo.count(foo[i])}
  => [1, 2, 3, 1, 3]
1.9.3p125 :004 > dup_indices
  => {1=>[0, 3], 3=>[2, 4]}

Sam