Re^5: sort direction

That result highly surprised me, because sort is optimized for the {$a <=> $b}, {$b <=> $a}, {$a cmp $b} and {$b cmp $a} blocks (in the sense it recognises those blocks and does the compare internally instead of calling the block).

But then I realized that the current sort implementation is also implemented to take advantage of long runs of increasing/decreasing values - and in particulary sorted arrays.

So I decided to run the benchmark again, this time with shuffled values:

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark 'cmpthese';
use List::Util 'shuffle';

our @data = shuffle 1 .. 10000;

cmpthese -1, {
    '<=>'  => q[@s1=sort{$b<=>$a} @data],
    ' - '  => q[@s2=sort{$b - $a} @data],
};

__END__
      Rate   -   <=>
 -  36.5/s   -- -30%
<=> 52.3/s  43%   --
[download]

That's what I'd expect.

Perl --((8:>*

Comment on Re^5: sort direction Select or Download Code

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Re^6: sort direction by BrowserUk (Patriarch) on Oct 12, 2005 at 09:08 UTC
Sigh. Fooled again :) Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal? "Science is about questioning the status quo. Questioning authority". The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.	[reply] [d/l]
Re^6: sort direction by BrowserUk (Patriarch) on Oct 12, 2005 at 09:21 UTC
Then again, if you eliminate the optimisation advantage; `#!/usr/bin/perl use strict; use warnings; use Benchmark 'cmpthese'; use List::Util 'shuffle'; our @data = shuffle 1 .. 10000; cmpthese -1, { '<=>' => q[@s1=sort sub{ $b<=>$a }, @data], ' - ' => q[@s2=sort sub{ $b - $a }, @data], }; __END__ P:\test>junk Rate <=> - <=> 36.9/s -- -2% - 37.4/s 2% -- P:\test>junk Rate - <=> - 36.3/s -- -3% <=> 37.4/s 3% -- P:\test>junk Rate - <=> - 35.8/s -- -0% <=> 35.8/s 0% -- P:\test>junk Rate <=> - <=> 36.8/s -- -0% - 36.9/s 0% --` [download] ... it makes no difference whether the block returns (-1,0,1) or (-n,0,n), which is more relavent to the original discussion. However, in C or asm, it might avoid an unnecessary booleanisation of a subtraction? Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal? "Science is about questioning the status quo. Questioning authority". The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.	[reply] [d/l]