From: "David A. Black" <dblack@...>
Date: 2007-08-19T22:06:54+09:00
Subject: Re: Detecting duplicates in an array, anything in the standard library ?

--1926193751-1394418063-1187528815=:15936
Content-Type: MULTIPART/MIXED; BOUNDARY="1926193751-1394418063-1187528815=:15936"

  This message is in MIME format.  The first part should be readable text,
  while the remaining parts are likely unreadable without MIME-aware tools.

--1926193751-1394418063-1187528815=:15936
Content-Type: TEXT/PLAIN; charset=X-UNKNOWN; format=flowed
Content-Transfer-Encoding: QUOTED-PRINTABLE

Hi --

On Sun, 19 Aug 2007, Ari Brown wrote:

>
> On Aug 19, 2007, at 6:39 AM, Thibaut Barr=E8re wrote:
>
>> Hi!
>>=20
>> Just wondering if there is something simple already built in the std
>> library to remove duplicates from an array (or an enumerable). I've
>> seen and used various approaches, like:
>>=20
>> module Enumerable
>>  def dups
>>    inject({}) {|h,v| h[v]=3Dh[v].to_i+1; h}.reject{|k,v| v=3D=3D1}.keys
>>  end
>> end
>>=20
>> which will give:
>>=20
>>> %w(a b c c).dups
>> =3D> ["c"]
>>=20
>> Anything more elegant ?
>
> Couldn't you also just do a union with itself?
>
> a =3D %w(a b c b a)
> b =3D a & a                #=3D> ["a", "b", "c"]
>
> Score one for me :-))

I think that just reinvents uniq (see my previous reinvention :-)

For what it's worth, here's a nice-looking but probably very
inefficient version:

module ArrayStuff
   def count(e)
     select {|f| f =3D=3D e }.size
   end

   def dups
     select {|e| count(e) > 1 }.uniq
   end
end

a =3D [1,2,3,3,4,5,2].extend(ArrayStuff)

p a.dups    # [2,3]


David

--=20
* Books:
   RAILS ROUTING (new! http://www.awprofessional.com/title/0321509242)
   RUBY FOR RAILS (http://www.manning.com/black)
* Ruby/Rails training
     & consulting:  Ruby Power and Light, LLC (http://www.rubypal.com)
--1926193751-1394418063-1187528815=:15936--
--1926193751-1394418063-1187528815=:15936--