Re: Faster regex to split a string into runs of similar characters?

in reply to Faster regex to split a string into runs of similar characters?

If you want to match all 256 byte values, you'll need the /s modifier. I thought this would just be more correct, but it also happen to be slightly faster (4% on my computer), certainly because it's faster to match anything rather than check that the character is different from "\n".

Beside that, why are you using look-ahead assertions? Isn't /((.)\2+)/g stricly identical to your regex? I don't see a performance difference with that though, so maybe perl optimizes away the look-ahead.

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Re^2: Faster regex to split a string into runs of similar characters? by BrowserUk (Patriarch) on Nov 21, 2016 at 10:43 UTC
If you want to match all 256 byte values, you'll need the /s modifier. Yes. /s not /m; I always mix those two up. why are you using look-ahead assertions? Isn't /((.)\2+)/g stricly identical to your regex? No. That won't match a single character 'run'. 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". The enemy of (IT) success is complexity. In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]
Re^3: Faster regex to split a string into runs of similar characters? by Eily (Monsignor) on Nov 21, 2016 at 10:50 UTC
No. That won't match a single character 'run'. Right. `/((.)\2*)/g` does though, and this time it is faster (by 12% on my computer).	[reply] [d/l]
Re^4: Faster regex to split a string into runs of similar characters? by BrowserUk (Patriarch) on Nov 21, 2016 at 11:31 UTC
/((.)\2)/g does though,* Huh:) How did I missed that?! ... faster (by 12% on my computer). Only 4% difference on mine under 5.10 or 5.22: ## this 5.10 [0]{} Perl> cmpthese -1,{a=>q[ 1 while $s =~ m[((?=(.))\2+)]sg;],b=>q[ +1 while $s =~ m[((.)\2)]sg;] };; Rate a b a 204/s -- -4% b 212/s 4% -- [0]{} Perl> cmpthese -1,{a=>q[ 1 while $s =~ m[((?=(.))\2+)]sg;],b=>q[ +1 while $s =~ m[((.)\2)]sg;] };; Rate a b a 204/s -- -4% b 212/s 4% -- [0]{} Perl> C:\test>\Perl22\bin\perl.exe \Perl22\bin\p1.pl [0]{} Perl> $s = join'', map{ chr( 65+rand(26) ) x rand( 100 ) } 1 .. +1000;; [0]{} Perl> cmpthese -1,{a=>q[ 1 while $s =~ m[((?=(.))\2+)]sg;],b=>q[ +1 while $s =~ m[((.)\2)]sg;] };; Rate a b a 229/s -- -3% b 235/s 3% -- [0]{} Perl> cmpthese -1,{a=>q[ 1 while $s =~ m[((?=(.))\2+)]sg;],b=>q[ +1 while $s =~ m[((.)\2)]sg;] };; Rate a b a 229/s -- -4% b 238/s 4% -- [download] A small, but consistent gain. Thanks. 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". The enemy of (IT) success is complexity. In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]

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