From: Nick Dokos <ndokos@gmail.com>
To: help-gnu-emacs@gnu.org
Subject: Re: How to count the number of occurrences of a character in a string?
Date: Mon, 12 Oct 2015 19:27:43 -0400 [thread overview]
Message-ID: <87d1wjy8eo.fsf@alphaville.usersys.redhat.com> (raw)
In-Reply-To: CAFyQvY29R-xpAWK6em9fedE1cqVVqRMj6rHsuYWmpp5Yn15feg@mail.gmail.com
Kaushal Modi <kaushal.modi@gmail.com> writes:
> I took it up as an elisp exercise and got the below (not sure if it is
> performance optimal for your application):
>
> The catch form returns the number of matches.
>
> (let ((char ?a)
> (str "abcda"))
> (catch 'break
> (let* ((str str)
> (len (length str))
> (num-matches 0)
> match-pos)
> (dotimes (i len)
> (setq match-pos (string-match-p (char-to-string char) str))
> (when match-pos
> (setq str (substring-no-properties str (1+ match-pos)))
> (setq len (length str))
> (setq num-matches (1+ num-matches)))
> (when (= 0 len)
> (throw 'break num-matches))))))
>
What happens if len never becomes 0 in the loop? E.g looking for "f" in
"falala" or "alala"? No throw, so catch returns nil: you probably want
to add another throw outside the loop; or (better) do something else
when match-pos is nil (there are no more matches), so you don't go
through the loop uselessly:
(if match-pos
(progn
(setq str ...)
(setq len ...)
(setq nm-matches))
(throw 'break num-matches))
But I suspect cl-count will be much faster.
Nick
next prev parent reply other threads:[~2015-10-12 23:27 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-12 19:45 How to count the number of occurrences of a character in a string? Marcin Borkowski
2015-10-12 21:43 ` Kaushal Modi
2015-10-12 23:27 ` Nick Dokos [this message]
2015-10-13 1:18 ` Stefan Monnier
2015-10-13 16:06 ` Kaushal Modi
2015-10-13 16:31 ` Kaushal Modi
2015-10-13 16:48 ` Eli Zaretskii
2015-10-13 17:41 ` Eli Zaretskii
2015-10-13 17:43 ` Kaushal Modi
2015-10-13 19:07 ` Eli Zaretskii
2015-10-13 19:56 ` Kaushal Modi
2015-10-13 20:17 ` Eli Zaretskii
2015-10-13 20:41 ` Kaushal Modi
[not found] ` <mailman.267.1444767491.7904.help-gnu-emacs@gnu.org>
2015-10-13 20:46 ` Brendan Halpin
2015-10-13 21:07 ` Kaushal Modi
[not found] ` <mailman.273.1444770543.7904.help-gnu-emacs@gnu.org>
2015-10-13 22:44 ` Joost Kremers
2015-10-14 10:04 ` Oleh Krehel
2015-10-14 17:06 ` Eli Zaretskii
2015-10-13 20:43 ` Michael Heerdegen
2015-10-13 20:59 ` Charles Curley
2015-10-14 18:19 ` Noam Postavsky
2015-10-14 20:00 ` Kaushal Modi
2015-10-13 22:00 ` Emanuel Berg
[not found] <mailman.164.1444679125.7904.help-gnu-emacs@gnu.org>
2015-10-12 23:35 ` Joost Kremers
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