From: wsnyder@wsnyder.org (Wilson Snyder)
To: emacs-devel@gnu.org
Subject: Suggestions to remove one alist's members from another
Date: Fri, 9 Apr 2010 08:27:08 -0400 (EDT) [thread overview]
Message-ID: <20100409122708.DCDB618838C@wsnyder.org> (raw)
Hello,
One of my packages has a function like this:
(defun not-in-alist (in-alist not-alist)
"Return alist of elements in IN-ALIST that aren't also in NOT-ALIST.
Also remove any duplicates in IN-ALIST."
(let (out-alist)
(while in-alist
(if (not (or (assoc (car (car in-alist)) not-alist)
(assoc (car (car in-alist)) out-alist)))
(setq out-alist (cons (car in-alist) out-alist)))
(setq in-alist (cdr in-alist)))
(nreverse out-alist)))
This code was expedient, but obviously not fast for large lists.
I want to replace it with something closer to O(1), even if it
has larger overhead.
Does anyone have an existing function or example I should use to
do this? It seems relatively primitive.
If not, my thought is this: when the list was over some size
I'd determine experimentally, it would instead build a hash
table from in-list and hit the not-alist against that. When
complete it would unfortunately require a second pass
through the in-alist to return it maintaining the original
order.
Thoughts?
Thanks
next reply other threads:[~2010-04-09 12:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-09 12:27 Wilson Snyder [this message]
2010-04-09 15:12 ` Suggestions to remove one alist's members from another David Kastrup
-- strict thread matches above, loose matches on Subject: below --
2010-04-09 13:02 Wilson Snyder
2010-04-09 14:11 ` Davis Herring
2010-04-09 14:16 ` Wilson Snyder
2010-04-09 14:45 ` Drew Adams
2010-04-09 14:48 ` Davis Herring
2010-04-09 15:05 ` David Kastrup
2010-04-09 17:31 ` Stephen J. Turnbull
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