Re: Sort command equivalent in perl

How about this?

use strict;
use warnings;
use File::Copy;
use Tie::File;

copy( $ARGV[0], $ARGV[1] ) or die $!;
my @file;
tie @file, 'Tie::File', $ARGV[1] or die $!;
@file = sort @file;
untie @file;
[download]

Tie::File has low memory requirements: The file's lines are treated as a disk-based array. File::Copy concisely copies the source file to a target filename. Then we tie the target file and sort it.

I can't vouch for it being particularly fast; I suspect the OS version of sort is better optimized for disk-based sorting.

Update: Ooh I hate when first instinct is misguided. Well, second instinct really, first instinct is to use the tools that are already written and proven (ie, the Linux sort utility). This muse fails as MidLife pointed out: The sort itself isn't done 'inline', and thus the memory usage will soar. And of course not even Evel Knievel could jump the valley separating the speed of the established tool versus this hack. :)

Dave

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Re^2: Sort command equivalent in perl by MidLifeXis (Monsignor) on Dec 16, 2011 at 16:56 UTC
Will the sort still happen in memory? If it is not in memory, I do not see how this can do the `@file = sort @file` without data loss. If it is in memory, we are back to the original problem. +1 for the unique approach. --MidLifeXis	[reply] [d/l]
Re^3: Sort command equivalent in perl by BrowserUk (Patriarch) on Dec 16, 2011 at 17:21 UTC
You're right. it wouldn't work for files greater than memory. I thought it might for a while because of the in-place sort optimisation that came in somewhere in 5.8.x, that means that: `@ar = sort @r;` [download] gets converted to `sort \@ar;` and sorts in place rather then copies the array to the stack and back. But looking at the code, it doesn't work for tied arrays: `/* optimiser converts "@a = sort @a" to "sort \@a"; * in case of tied @a, pessimise: push (@a) onto stack, then assig +n * result back to @a at the end of this function */` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l] [select]
Re^4: Sort command equivalent in perl by davido (Cardinal) on Dec 16, 2011 at 17:25 UTC
Yup, there's the gotcha that gotme. :) I remembered that `@array = sort @array` doesn't make a copy, but failed to think through the fact that tie would be different. Dave	[reply] [d/l]
Re^2: Sort command equivalent in perl by BrowserUk (Patriarch) on Dec 16, 2011 at 16:55 UTC
I can't vouch for it being particularly fast; That is really, really, really, really() S-L-O-W-!-!-!-!. ()And I do mean re-ea-al-ll-ly sl-lo-ow! Like pre-climate change glacial man. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply]