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devel / comp.lang.lisp / Faster remove-duplicates with sorted list.

Faster remove-duplicates with sorted list.

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https://www.rocksolidbbs.com/devel/article-flat.php?id=16831&group=comp.lang.lisp#16831

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From: No_spamming@noWhere_7073.org (Robert L.)
Newsgroups: comp.lang.lisp
Subject: Faster remove-duplicates with sorted list.
Date: Fri, 11 Feb 2022 16:55:32 -0000 (UTC)
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by: Robert L. - Fri, 11 Feb 2022 16:55 UTC

> (defun uniquify-sorted-list (list &key (key #'identity) (test #'eql))
> (loop for element in list
> for element-key = (funcall key element)
> for last-element-key = (load-time-value (gensym))
> then element-key
> unless (funcall test element-key last-element-key)
> collect element))

Gauche Scheme:

(define (destutter seq :optional (test equal?) (key values))
(if (or (null? seq) (null? (cdr seq)))
seq
(let ((ab (take seq 2)))
(if (apply test (map key ab))
(destutter (cdr seq) test key)
(cons (car ab) (destutter (cdr seq) test key))))))

(destutter '(0 0 1 2 3 3 3 4 5))
===>
(0 1 2 3 4 5)

(destutter '(0 0 2 3 5 7 6 8) eq? odd?)
===>
(2 7 8)

Subject	Author
Faster remove-duplicates with sorted list.	Robert L.