From: "David A. Black" <dblack@...>
Date: 2007-08-22T01:26:04+09:00
Subject: Re: Detecting duplicates in an array, anything in the standa

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Hi --

On Wed, 22 Aug 2007, Phrogz wrote:

> On Aug 21, 10:04 am, Ari Brown <a...@aribrown.com> wrote:
>> On Aug 21, 2007, at 4:59 AM, Pe=F1a, Botp wrote:
>>
>>> From: Robert Klemme [mailto:shortcut...@googlemail.com]
>>> # irb(main):002:0> a.uniq.select{|e| (a-[e]).size < a.size - 1}
>>
>>> compare also,
>>
>>> irb(main):056:0> b=3Da.dup
>>> =3D> [1, 1, 2, 2, 2, 4, 3]
>>> irb(main):057:0> b.uniq.select{|e| (b.reject!{|f| f =3D=3D e}).size > 1=
}
>>> =3D> [1, 2]
>>
>> I still think it's easier just to union itself...
>>
>> a =3D [1,2,3,2,1]
>> b =3D a & a
>> b =3D [1,2,3]
>
> ...but that's not what the OP wanted. What you've written is the same
> as the #uniq method.
>
> Don't feel bad, this thread has been filled with people answering the
> wrong question. :p The original question was roughly "How do I find
> out all the elements in the array that are duplicates?"
>
> Solutions to that question would not include '3' in the above results.
> It's unclear to me if %w| a b b b | should include 'b' once or twice
> in the output, though, and the original poster has not clarified that,
> that I can see.

I think once, since it's just the quality of being non-unique in
the array that qualifies an object for inclusion. At least, that's my
understanding, though as one of the people who reimplemented
Array#uniq, I may not be the right person to listen to :-)


David

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