GNU bug report logs - #19896
23.1; reverse-region is slow compared to sort-columns

Previous Next

To add a comment to this bug, you must first unarchive it, by sending
a message to control AT debbugs.gnu.org, with unarchive 19896 in the body.
You can then email your comments to 19896 AT debbugs.gnu.org in the normal way.

Toggle the display of automated, internal messages from the tracker.

Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: asparagus <at> comcast.net
To: bug-gnu-emacs <at> gnu.org
Subject: 23.1; reverse-region is slow compared to sort-columns
Date: Wed, 18 Feb 2015 17:35:42 +0000 (UTC)

The emacs manual recommends 'M-x reverse-region' as a companion to 'M-x sort-columns' to achieve a descending-order column sort.  However, for large regions (>100k lines), 'M-x reverse-region' is noticeably slower than 'M-x sort-columns', making descending sort much slower than ascending sort.

A workaround on linux: use 'C-u M-x shell-command-on-region' with tac (the opposite of cat) instead of using 'M-x reverse-region'.

FROM THE MANUAL:
https://www.gnu.org/software/emacs/manual/html_node/emacs/Sorting.html
M-x reverse-region
    Reverse the order of the lines in the region. This is useful for sorting into descending order by fields or columns, since those sort commands do not have a feature for doing that.

Message #8 received at 19896 <at> debbugs.gnu.org (full text, mbox):

From: Ivan Shmakov <ivan <at> siamics.net>
To: 19896 <at> debbugs.gnu.org, asparagus <at> comcast.net
Subject: Re: bug#19896: 23.1; reverse-region is slow compared to sort-columns 
Date: Wed, 18 Feb 2015 18:29:08 +0000

>>>>> asparagus  <asparagus <at> comcast.net> writes:

 > The emacs manual recommends 'M-x reverse-region' as a companion to
 > 'M-x sort-columns' to achieve a descending-order column sort.

	This could be a bug in the manual, as sort-columns has an
	optional (prefix) ‘reverse’ argument since at least 1990
	(d32200ac.)

 > However, for large regions (> 100k lines), 'M-x reverse-region' is
 > noticeably slower than 'M-x sort-columns', making descending sort
 > much slower than ascending sort.

	I don’t seem to see this on the current master; at a glance,
	M-x reverse-region takes less time to complete than
	M-x sort-columns.

	The current stable version of Emacs is 24.4, with the pretest
	for 24.5 being available since 17th [1].  Could you please check
	if this issue also manifests with either of these versions?

	TIA.

[1] news:87mw4c6gjn.fsf <at> petton.fr
    http://permalink.gmane.org/gmane.emacs.devel/183187

 > A workaround on linux: use 'C-u M-x shell-command-on-region' with tac
 > (the opposite of cat) instead of using 'M-x reverse-region'.

	On a GNU system (as well as on any other system featuring
	GNU Coreutils), it should be possible to just use sort(1) for
	the purpose.  For instance, the “reverse” option is ‘-r’.

[…]

-- 
FSF associate member #7257  http://boycottsystemd.org/  … 3013 B6A0 230E 334A

Message #11 received at 19896 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Ivan Shmakov <ivan <at> siamics.net>
Cc: 19896 <at> debbugs.gnu.org
Subject: Re: bug#19896: 23.1; reverse-region is slow compared to sort-columns
Date: Wed, 18 Feb 2015 21:01:15 +0200

> From: Ivan Shmakov <ivan <at> siamics.net>
> Date: Wed, 18 Feb 2015 18:29:08 +0000
> 
>  > A workaround on linux: use 'C-u M-x shell-command-on-region' with tac
>  > (the opposite of cat) instead of using 'M-x reverse-region'.
> 
> 	On a GNU system (as well as on any other system featuring
> 	GNU Coreutils), it should be possible to just use sort(1) for
> 	the purpose.  For instance, the “reverse” option is ‘-r’.

But sort(1)'s sort order is locale-specific, whereas that of Emacs
isn't.

Message #14 received at 19896 <at> debbugs.gnu.org (full text, mbox):

From: Ivan Shmakov <ivan <at> siamics.net>
To: 19896 <at> debbugs.gnu.org
Subject: Re: bug#19896: 23.1; reverse-region is slow compared to sort-columns 
Date: Wed, 18 Feb 2015 19:13:00 +0000

>>>>> Eli Zaretskii <eliz <at> gnu.org> writes:
>>>>> From: Ivan Shmakov  Date: Wed, 18 Feb 2015 18:29:08 +0000

[…]

 >> On a GNU system (as well as on any other system featuring GNU
 >> Coreutils), it should be possible to just use sort(1) for the
 >> purpose.  For instance, the “reverse” option is ‘-r’.

 > But sort(1)'s sort order is locale-specific, whereas that of Emacs
 > isn't.

	How is that a disadvantage?  The user can easily force any
	locale of those available on the system with an explicit
	LC_ALL=, like:

$ LC_ALL=de_DE.UTF-8 sort < list.de 

$ LC_ALL=ru_RU.UTF-8 sort < list.ru 

$ LC_ALL=C sort < list.ascii 

	For one thing, M-x sort-lines seems to put ё after я, while in
	Russian it comes between е and ж.  And similarly for ß (and the
	accented letters) in German, etc.

-- 
FSF associate member #7257  np. Bombtrack — clawz/bomb  … 3013 B6A0 230E 334A

Message #17 received at 19896 <at> debbugs.gnu.org (full text, mbox):

From: asparagus <at> comcast.net
To: 19896 <at> debbugs.gnu.org
Subject: bug#19896
Date: Wed, 18 Feb 2015 19:19:42 +0000 (UTC)

[Message part 1 (text/plain, inline)]

Thanks for identifying the bug in the manual. 

I do not have access to the latest versions of emacs, but thank you for verifying that reverse-region has an efficient implementation in the latest version. 

Given that reverse-region is efficiently implemented in the latest versions, correcting the manual entries for sort-columns and reverse-region would provide resolution to this issue. 

[Message part 2 (text/html, inline)]

Message #20 received at 19896 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Ivan Shmakov <ivan <at> siamics.net>
Cc: 19896 <at> debbugs.gnu.org
Subject: Re: bug#19896: 23.1; reverse-region is slow compared to sort-columns
Date: Wed, 18 Feb 2015 21:29:13 +0200

> From: Ivan Shmakov <ivan <at> siamics.net>
> Date: Wed, 18 Feb 2015 19:13:00 +0000
> 
> >>>>> Eli Zaretskii <eliz <at> gnu.org> writes:
> >>>>> From: Ivan Shmakov  Date: Wed, 18 Feb 2015 18:29:08 +0000
> 
> […]
> 
>  >> On a GNU system (as well as on any other system featuring GNU
>  >> Coreutils), it should be possible to just use sort(1) for the
>  >> purpose.  For instance, the “reverse” option is ‘-r’.
> 
>  > But sort(1)'s sort order is locale-specific, whereas that of Emacs
>  > isn't.
> 
> 	How is that a disadvantage?

I didn't say it was a disadvantage, only that the results might be
different, and will almost certainly be different in different
locales.

>       The user can easily force any locale of those available on the
> 	system with an explicit LC_ALL=, like:
> 
> $ LC_ALL=de_DE.UTF-8 sort < list.de 
> 
> $ LC_ALL=ru_RU.UTF-8 sort < list.ru 
> 
> $ LC_ALL=C sort < list.ascii 

Yes, but Emacs's sort order is not in any locale, more or less.  So
it's not easy to find a locale that will produce the same order as
Emacs, unless you know a lot about Emacs internals.  And even if you
do, such a locale might not be installed on the end-user's machine.

> 	For one thing, M-x sort-lines seems to put ё after я, while in
> 	Russian it comes between е and ж.  And similarly for ß (and the
> 	accented letters) in German, etc.

Precisely!  That was my point.

Message #23 received at 19896 <at> debbugs.gnu.org (full text, mbox):

From: asparagus <at> comcast.net
To: 19896 <at> debbugs.gnu.org
Subject: Please modify documentation to close this bug
Date: Thu, 26 Feb 2015 17:53:48 +0000 (UTC)

To close this bug, please modify
https://www.gnu.org/software/emacs/manual/html_node/emacs/Sorting.html
as follows:

Add the following to the description of M-x sort-columns:
"A numeric argument means sort into descending order."

Remove "or columns" from the description of M-x reverse-region.

Thanks.

Message #28 received at 19896-done <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: 19896-done <at> debbugs.gnu.org
Subject: Re: bug#19896: Please modify documentation to close this bug
Date: Sat, 18 Apr 2015 20:49:10 -0400

Version: 25.1

asparagus <at> comcast.net wrote:

> Add the following to the description of M-x sort-columns:
> "A numeric argument means sort into descending order."
>
> Remove "or columns" from the description of M-x reverse-region.

Thanks; done in the source. (The versions on www.gnu.org will probably
not be updated until the next Emacs release.)

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.