From: John Wiegley <jwiegley@gmail.com>
To: emacs-devel@gnu.org
Subject: Any interest in a function like this to add to subr.el?
Date: Tue, 18 Oct 2016 10:53:10 -0700 [thread overview]
Message-ID: <m2mvi17ddl.fsf@newartisans.com> (raw)
(defun sort-on (seq predicate accessor)
"Sort SEQ use PREDICATE applied to values returned by ACCESSOR.
This implements the so-called Schwartzian transform, which has
the performance advantage of applying ACCESSOR at most once per
element in the list, as opposed to using `sort' with a PREDICATE
that applies the ACCESSOR.
Note: this function is only a win over `sort' if ACCESSOR is
compute-intensive; otherwise, it uses more intermediate cons
cells than regular `sort', and so represents a memory for CPU
tradeoff."
(mapcar #'cdr (sort (mapcar #'(lambda (x) (cons (funcall accessor x) x)) seq)
#'(lambda (x y) (funcall predicate (car x) (car y))))))
--
John Wiegley GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com 60E1 46C4 BD1A 7AC1 4BA2
next reply other threads:[~2016-10-18 17:53 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-18 17:53 John Wiegley [this message]
2016-10-18 20:13 ` Any interest in a function like this to add to subr.el? Dmitry Gutov
2016-10-18 20:34 ` John Wiegley
2016-10-18 21:09 ` Dmitry Gutov
2016-10-18 21:25 ` John Wiegley
2016-10-19 5:01 ` Ken Raeburn
2016-10-19 6:02 ` John Wiegley
2016-10-19 14:51 ` Stefan Monnier
2016-10-19 14:48 ` Stefan Monnier
2016-10-19 23:12 ` Dmitry Gutov
2016-10-20 1:48 ` Stefan Monnier
2016-10-19 13:46 ` Andy Moreton
2016-10-19 14:52 ` Stefan Monnier
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