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Re: What to do for faster `remove-duplicates'?
From: |
Oleh Krehel |
Subject: |
Re: What to do for faster `remove-duplicates'? |
Date: |
Wed, 06 May 2015 21:32:52 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
Artur Malabarba <address@hidden> writes:
> 2015-05-06 19:41 GMT+01:00 Oleh Krehel <address@hidden>:
>> Artur Malabarba <address@hidden> 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.
You're right. I've pushed the corrected version. I tried testing with
benchmark-run and the same large collection. The time fluctuates too
much to judge which method is better. They're roughly equal, and the
intuition is that not using `nreverse` is better.
Oleh
- Re: What to do for faster `remove-duplicates'?, (continued)
- Re: What to do for faster `remove-duplicates'?, Stefan Monnier, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Oleh Krehel, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Stefan Monnier, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Oleh Krehel, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Thierry Volpiatto, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Oleh Krehel, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Artur Malabarba, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Artur Malabarba, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Oleh Krehel, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Artur Malabarba, 2015/05/06
- Re: What to do for faster `remove-duplicates'?,
Oleh Krehel <=
- Re: What to do for faster `remove-duplicates'?, Artur Malabarba, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Thierry Volpiatto, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Stefan Monnier, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Stefan Monnier, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Artur Malabarba, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Artur Malabarba, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Oleh Krehel, 2015/05/06
- Re: What to do for faster `remove-duplicates'?, Artur Malabarba, 2015/05/06