From: David Alan Black <dblack@...>
Date: 2000-12-03T22:15:32+09:00
Subject: [ruby-talk:6764] Re: Array Intersect (&) question

Hello --

On Sun, 3 Dec 2000 peter.wood@worldonline.dk wrote:

> I agree with Ross.  Presumably, if you are intersecting "pseudo-sets"
> with duplicates, you WANT the duplicates.  Ruby should not second
> guess you.  If you don't want the duplicates, you can easily remove
> them, but its trickier to go the other way.
> 
> (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))

And order is significant, though (not(or(to digress into Lisp)anything))
the significance varies among Lisps.

GNU Common Lisp:

>(intersection '(1 1 2) '(1 2 2))
(2 1 1)

>(intersection '(1 2 2) '(1 1 2))
(2 2 1)


Emacs Lisp:

(intersection '(1 1 2) '(1 2 2))  => (2 2 1)
(intersection '(1 2 2) '(1 1 2))  => (2 1 1)


Funnily enough, this discussion takes me back to my Jotto program,
which was my first non-trivial... well, non-very-short... Ruby
program, and where one of the playing modes requires adding up how
many letters the two words have, regardless of position in the words.
The question being: how many letters do "agree" and "anger" have in
common, and does it matter which is the guess and which the guessee?
(Not that I care much -- I always play the position-sensitive version
anyway :-)


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav