From: Sean O'Halpin <sean.ohalpin@...>
Date: 2007-10-28T22:12:18+09:00
Subject: Re: Duplicate elements in array

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On 10/28/07, Shuaib Zahda <shuaib.zahda@gmail.com> wrote:
>
> Hello
>
> I am trying to output the duplicate elements in an array. I looked into
> the api of ruby I found uniq method which outputs the array with no
> duplication. What i want is to know which elements is duplicated.
> For example
>
> array = ["apple", "banana", "apple", "orange"]
> => ["apple", "banana", "apple", "orange"]
> array.uniq
> => ["apple", "banana", "orange"]
>
> I want the method to tell me that apple is the duplicated element
>
> I tried this but it does not work
>
> array - array.uniq
>
> any idea
>
> Regards
> Shuaib
> --
> Posted via http://www.ruby-forum.com/.
>
> Here's one way (I'm sure there must be a simpler approach - just can't
think of it right now):

array = ["apple", "banana", "apple", "orange"]
counts = array.inject(Hash.new {|h,k| h[k] = 0 }) { |hash, item| hash[item]
+= 1; hash}
p counts #=> {"apple"=>2, "banana"=>1, "orange"=>1}
p counts.select { |k,v| v > 1 }.map{ |k, v| k}.flatten #=> ["apple"]


Regards,
Sean

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