From: Artur Malabarba <bruce.connor.am@gmail.com>
To: Oleh Krehel <ohwoeowho@gmail.com>
Cc: emacs-devel <emacs-devel@gnu.org>,
Thierry Volpiatto <thierry.volpiatto@gmail.com>
Subject: Re: What to do for faster `remove-duplicates'?
Date: Wed, 6 May 2015 20:24:42 +0100 [thread overview]
Message-ID: <CAAdUY-KYWsHuqn6qFeVaFzPfZRp6O70Q+Lfi8UdQzfiwUK02rg@mail.gmail.com> (raw)
In-Reply-To: <87lhh1zgyn.fsf@gmail.com>
2015-05-06 19:41 GMT+01:00 Oleh Krehel <ohwoeowho@gmail.com>:
> Artur Malabarba <bruce.connor.am@gmail.com> writes:
>
>> But that nreverse could be optimized out if the first loop followed a
>> `while'+`setcdr' strategy like the second.
>
> Please check the optimized version:
>
> (defun delete-dups (list)
> "Destructively remove `equal' duplicates from LIST.
> Store the result in LIST and return it. LIST must be a proper list.
> Of several `equal' occurrences of an element in LIST, the first
> one is kept."
> (if (> (length list) 100)
> (let ((hash (make-hash-table :test #'equal)))
> (let ((tail list)
> elt retail)
> (while (setq retail (cdr tail))
> (setq elt (car retail))
> (if (gethash elt hash)
> (setcdr tail (cdr retail))
> (puthash elt t hash))
> (setq tail retail))))
> (let ((tail list))
> (while tail
> (setcdr tail (delete (car tail) (cdr tail)))
> (setq tail (cdr tail)))))
> list)
I may be wrong, but it looks like it's completely skipping the car of the list.
next prev parent reply other threads:[~2015-05-06 19:24 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-06 7:33 What to do for faster `remove-duplicates'? Oleh Krehel
2015-05-06 12:59 ` Stefan Monnier
2015-05-06 13:30 ` Oleh Krehel
2015-05-06 13:50 ` Stefan Monnier
2015-05-06 13:51 ` Oleh Krehel
2015-05-06 17:43 ` Thierry Volpiatto
2015-05-06 17:54 ` Oleh Krehel
2015-05-06 18:31 ` Artur Malabarba
2015-05-06 18:33 ` Artur Malabarba
2015-05-06 18:41 ` Oleh Krehel
2015-05-06 19:24 ` Artur Malabarba [this message]
2015-05-06 19:32 ` Oleh Krehel
2015-05-06 21:22 ` Artur Malabarba
2015-05-06 18:48 ` Thierry Volpiatto
2015-05-06 20:54 ` Stefan Monnier
2015-05-06 20:54 ` Stefan Monnier
2015-05-06 21:18 ` Artur Malabarba
2015-05-06 14:04 ` Artur Malabarba
2015-05-06 14:13 ` Oleh Krehel
2015-05-06 14:49 ` Artur Malabarba
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