rotten news relay - comp.lang.lisp - P16 (**) Drop every N'th element from a list.

Subject: P16 (**) Drop every N'th element from a list.
From: B. Pym
Newsgroups: comp.lang.lisp
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Date: Mon, 2 Sep 2024 07:10 UTC

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From: Nobody447095@here-nor-there.org (B. Pym)
Newsgroups: comp.lang.lisp
Subject: P16 (**) Drop every N'th element from a list.
Date: Mon, 2 Sep 2024 07:10:35 -0000 (UTC)
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> Example:
> * (drop '(a b c d e f g h i k) 3)

Where is "j"?

> (A B D E G H K)
> "

> (defun drop (list n)
> (loop
> :for elt :in list
> :for i :from 1
> :for die-elt-die! = (zerop (mod i n))
> :unless die-elt-die!
> :collect elt))

Gauche Scheme

(use srfi-1) ;; circular-list

(define (dropnth xs n)
(filter-map
(lambda (x b) (and b x))
xs
(cdr (apply circular-list #f (make-list (- n 1) #t)))))

(dropnth '(a b c d e f g h i j k l m) 3)
===>
(a b d e g h j k m)

Subject	Author
P16 () Drop every N'th element from a list.**	B. Pym

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comp / comp.lang.lisp / P16 (**) Drop every N'th element from a list.