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Last active September 18, 2019 11:21
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dolist vs mapcar
;;; dashtest.el --- benchmarking dash -*- lexical-binding: t -*-
(defmacro --map-mapcar (form list)
(declare (debug (form form)))
`(mapcar (lambda (it) ,form) ,list))
(defmacro --map-loop (form list)
(declare (debug (form form)))
(let ((result-sym (make-symbol "result")))
`(let (,result-sym)
(dolist (it ,list)
(push ,form ,result-sym))
(nreverse ,result-sym))))
(defun wh/benchmark ()
(let ((small-list (-repeat 1 'foo))
(medium-list (-repeat 1000 'foo))
(large-list (-repeat 100000 'foo)))
"Small list with mapcar (seconds): %s"
(car (benchmark-run 10 (--map-mapcar it small-list))))
"Small list with loop (seconds): %s"
(car (benchmark-run 10 (--map-loop it small-list))))
"Medium list with mapcar (seconds): %s"
(car (benchmark-run 10 (--map-mapcar it medium-list))))
"Medium list with loop (seconds): %s"
(car (benchmark-run 10 (--map-loop it medium-list))))
"Large list with mapcar (seconds): %s"
(car (benchmark-run 10 (--map-mapcar it large-list))))
"Large list with loop (seconds): %s"
(car (benchmark-run 10 (--map-loop it large-list))))))
;; Small list with mapcar (seconds): 1.0259000000000001e-05
;; Small list with loop (seconds): 2.8387e-05
;; Medium list with mapcar (seconds): 0.0027399819999999997
;; Medium list with loop (seconds): 0.007948615
;; Large list with mapcar (seconds): 0.7446324980000001
;; Large list with loop (seconds): 1.236648743
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abo-abo commented Mar 6, 2017

I got with emacs -batch -l mapcar-test.elc (replace -repeat with make-list):

Small list with mapcar (seconds): 4.476e-06
Small list with loop (seconds): 2.7050000000000004e-06
Medium list with mapcar (seconds): 0.000566982
Medium list with loop (seconds): 0.00086927
Large list with mapcar (seconds): 0.098213352
Large list with loop (seconds): 0.162408572

Overall, not surprising. But the loop is faster for the small list on my system.

Here, dolist and mapcar are used for consing a list - dolist would be faster than mapcar if you were accumulating instead of consing.

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