From: Mark Van Holstyn <mvette13@...>
Date: 2005-10-17T15:38:33+09:00
Subject: Re: How to get non-unique elements from an array?

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Zach, if an element repeats more that once, itll double up in the output
array. need to add a .uniq on the end

irb(main):165:0> a =3D [1,2,3,4,5,3,5,3,5]
=3D> [1, 2, 3, 4, 5, 3, 5, 3, 5]
irb(main):166:0> t=3D[]; a.delete_if{ |e| r=3D(not t.include? e); t.push(e)=
; r }
=3D> [3, 5, 3, 5]

That aside, this one is a little shorter, and seems to benchmark a touch
faster as well.

irb(main):180:0> a=3D[1,2,3,4,5,3,5,3,5]
=3D> [1, 2, 3, 4, 5, 3, 5, 3, 5]
irb(main):181:0> t=3D[]; a.select{ |e| r=3Dt.include?e; t<<e; r }.uniq
=3D> [3, 5]
irb(main):182:0> a
=3D> [1, 2, 3, 4, 5, 3, 5, 3, 5]

Mark

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