Re: Re: Array How to/Performance: mass initialization or update using array slice

Off the top of my head I seem to recall that the slice operation is quicker than using a loop as most of the work is being done in C rather transitioning between C and perl as with a loop. However, you would probably need to be setting a few hundred elements of the array at a time, and/or doing this very often before you would notice the difference in runtime of your script.

That said, the slice method is very clean syntactically, so there is no reason not to use it, and any performance benefit never hurts, and is a nice bonus.

Examine what is said, not who speaks.

"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller

Comment on Re: Re: Array How to/Performance: mass initialization or update using array slice

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Re: Re: Re: Array How to/Performance: mass initialization or update using array slice by Anonymous Monk on Jun 21, 2003 at 10:34 UTC
#!/usr/bin/perl -w -- use strict; use Benchmark 'cmpthese'; cmpthese(-3,{ 'perloop' => sub { my @array; for(0..49) { $array[$_]=50; } return(); }, 'c-loop' => sub { my @array; for(my $i=0; $i<50; $i++) { $array[$i]=50; } return(); }, 'rangeslice' => sub { my @array; @array[0..49] = (50) x 50; return(); }, 'literalslice' => sub { my @array; @array[ 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20, 21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37, 38,39,40,41,42,43,44,45,46,47,48,49 ] = ( 50,50,50,50,50,50,50,50,50,50,50, 50,50,50,50,50,50,50,50,50,50,50, 50,50,50,50,50,50,50,50,50,50,50, 50,50,50,50,50,50,50,50,50,50,50, 50,50,50,50,50,50 ); return(); }, 'literalassign' => sub { my @array = ( 50,50,50,50,50,50,50,50,50,50,50, 50,50,50,50,50,50,50,50,50,50,50, 50,50,50,50,50,50,50,50,50,50,50, 50,50,50,50,50,50,50,50,50,50,50, 50,50,50,50,50,50 ); return(); }, 'repeatassign' => sub { my @array = (50) x 50; return(); }, }); __END__ Benchmark: running c-loop, literalassign, literalslice, perloop, range +slice, repeatassign, each for at least 3 CPU seconds... c-loop: 3 wallclock secs ( 3.39 usr + 0.00 sys = 3.39 CPU) @ + 31973.75/s (n=108391) literalassign: 4 wallclock secs ( 3.09 usr + 0.00 sys = 3.09 CPU) @ + 122232.14/s (n=378064) literalslice: 4 wallclock secs ( 3.00 usr + 0.00 sys = 3.00 CPU) @ + 92383.00/s (n=277149) perloop: 4 wallclock secs ( 3.00 usr + 0.00 sys = 3.00 CPU) @ + 40371.54/s (n=121155) rangeslice: 3 wallclock secs ( 3.02 usr + 0.00 sys = 3.02 CPU) @ + 65742.71/s (n=198280) repeatassign: 4 wallclock secs ( 3.19 usr + 0.00 sys = 3.19 CPU) @ + 129130.18/s (n=411667) Rate c-loop perloop rangeslice literalslice literala +ssign repeatassign c-loop 31974/s -- -21% -51% -65% + -74% -75% perloop 40372/s 26% -- -39% -56% + -67% -69% rangeslice 65743/s 106% 63% -- -29% + -46% -49% literalslice 92383/s 189% 129% 41% -- + -24% -28% literalassign 122232/s 282% 203% 86% 32% + -- -5% repeatassign 129130/s 304% 220% 96% 40% + 6% -- [download]	[reply] [d/l]
Re: Re: Re: Array How to/Performance: mass initialization or update using array slice by Anonymous Monk on Jun 21, 2003 at 09:02 UTC
Oh I see. I guess I'll do a test and see how big the difference would be. Thank you again.	[reply]