From: rpmohn@... (Ross Mohn)
Date: 2000-12-04T20:40:02+09:00
Subject: [ruby-talk:6800] Re: Array Intersect (&) question

matz@zetabits.com (Yukihiro Matsumoto) wrote in
<E142aoS-0004ty-00@ev.netlab.zetabits.co.jp>: 

>|(How do other languages do it? Common Lisp preserves the duplicates,
>|in the way Ross wants:
>|
>|(intersection '(1 1 y) '(1 y 1 z)) 
>|=> (1 1 y))
>
>I feel neither
>
>>(intersection '(1 1 2) '(1 2 2))
>(2 1 1)
>
>nor
>
>>(intersection '(1 1 2) '(1 2 2))
>(2 2 1)
>
>is natural intersection.  Both make me suspect easy implementation.
>Probably proper intersection is '(1 2) for this case.
>
>                                   matz.

Yes, (1 2) is definitely the proper intersection in this case. Your 
intersection would not contain duplicates unless BOTH sets had the 
duplicate: 
(intersection '(1 1 2) '(1 2 1 2))
(1 1 2)

-RPM
-- 
Ross Mohn
rpmohn@panix.com