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Re: A regex that only matches at offset that are multiples of a given N?

by johngg (Abbot)
on Feb 13, 2013 at 23:16 UTC ( #1018656=note: print w/ replies, xml ) Need Help??


in reply to A regex that only matches at offset that are multiples of a given N?

I think smls might be on the right track with moving pos. This benchmark seems to show that there is, if anything, a performance gain. I tried a modification to my first attempt my removing the duplicate matches via a hash but it only showed a marginal improvement in performance.

Then again, I am not very good at benchmarks so I could have cocked it up :-/

use strict; use warnings; use 5.014; use Benchmark qw{ cmpthese }; my $n = 4; my $str = q{x} x 50; substr $str, $_, 4, q{fred} for 4, 9, 20, 24, 31, 40; say qq{String: $str\n}; my $rcMovePos = sub { my $raMatches; while ( $str =~ m{\G(?:.{$n})*?(?=(fred.*))}g ) { push @{ $raMatches }, [ pos( $str ), $1 ]; pos $str += $n; } return $raMatches; }; my $rcNoDups = sub { my $rhMatches; $rhMatches->{ pos( $str ) } = $1 while $str =~ m{\G(?:.{$n})*?(?=(fred.*))}g; return $rhMatches; }; my $rcWithDups = sub { my $raMatches; push @{ $raMatches }, [ pos( $str ), $1 ] while $str =~ m{\G(?:.{$n})*?(?=(fred.*))}g; return $raMatches; }; my $raRes = $rcMovePos->(); say q{Using $rcMovePos}; say qq{ Matched $_->[ 1 ] at position $_->[ 0 ]} for @{ $raRes }; my $rhRes = $rcNoDups->(); say q{Using $rcNoDups}; say qq{ Matched $rhRes->{ $_ } at position $_} for sort { $a <=> $b } keys %{ $rhRes }; $raRes = $rcWithDups->(); say q{Using $rcWithDups}; say qq{ Matched $_->[ 1 ] at position $_->[ 0 ]} for @{ $raRes }; srand 1234567890; $str = q{x} x 10000; substr $str, int rand 9997, 4, q{fred} for 1 .. 50; say q{}; cmpthese( -5, { movePos => $rcMovePos, noDups => $rcNoDups, withDups => $rcWithDups, } );
String: xxxxfredxfredxxxxxxxfredfredxxxfredxxxxxfredxxxxxx Using $rcMovePos Matched fredxfredxxxxxxxfredfredxxxfredxxxxxfredxxxxxx at position 4 Matched fredfredxxxfredxxxxxfredxxxxxx at position 20 Matched fredxxxfredxxxxxfredxxxxxx at position 24 Matched fredxxxxxx at position 40 Using $rcNoDups Matched fredxfredxxxxxxxfredfredxxxfredxxxxxfredxxxxxx at position 4 Matched fredfredxxxfredxxxxxfredxxxxxx at position 20 Matched fredxxxfredxxxxxfredxxxxxx at position 24 Matched fredxxxxxx at position 40 Using $rcWithDups Matched fredxfredxxxxxxxfredfredxxxfredxxxxxfredxxxxxx at position 4 Matched fredxfredxxxxxxxfredfredxxxfredxxxxxfredxxxxxx at position 4 Matched fredfredxxxfredxxxxxfredxxxxxx at position 20 Matched fredfredxxxfredxxxxxfredxxxxxx at position 20 Matched fredxxxfredxxxxxfredxxxxxx at position 24 Matched fredxxxfredxxxxxfredxxxxxx at position 24 Matched fredxxxxxx at position 40 Matched fredxxxxxx at position 40 Rate withDups noDups movePos withDups 2321/s -- -3% -33% noDups 2394/s 3% -- -31% movePos 3445/s 48% 44% --

I hope this is of interest.

Cheers,

JohnGG


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