From: "pauldacus@..." <pauldacus@...>
Date: 2005-10-18T01:03:06+09:00
Subject: Re: How to get non-unique elements from an array?

Young grasshoppers... let us never forget the power of the REGEX!  Let
us not bother with counters or blocks... let us GSUB this bad boy!

a = [0,1,2,3,4,5,2,3]

a.sort.to_s.gsub(/(.)(\1)+/, '').split(//)

=>["0", "1", "4", "5"]

Sure... it returns the elements as strings, but a quick "to_i" call in
the inevitable iterator that is coming solves that.  This thing is also
subject to a Schwartzian Transform of the "map-sort-map" type.

Paul Dacus

Sam Kong 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.
>
> h = {}
> a.each do |i|
>   if h[i]
>     h[i] += 1
>   else
>     h[i] = 1
>   end
> end
>
> u = []
> h.each do |k, v|
>   if v > 1
>     u << k
>   end
> end
>
> #now u == [2,3]
>
> This works fine.
> But I think there's a better way.
> How do you handle such a case?
> 
> Thanks in advance.
> 
> Sam