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Re: Efficient selection mechanism?

by oiskuu (Hermit)
on Jan 14, 2014 at 23:01 UTC ( #1070624=note: print w/replies, xml ) Need Help??


in reply to Efficient selection mechanism?

Here's a small bench to highlight the speed difference in some of the chosen strategies.
#! /usr/bin/perl -wl use Benchmark 'cmpthese'; my (@v, @b); @v[0 .. 19] = 'a' .. 'z'; for (1..1e6) { my %r; undef $r{$v[rand @v]} until keys %r == 4; push @b, join '', keys %r; } my @AoA = map [map ord()-97, split //,$_], @b; my @vectors; for my $t (@v) { push @vectors, pack "b*", pack "c*", map !!/$t/, @b; } my $AoA = pack 'C*', map @$_, @AoA; cmpthese -5, { bitmap => sub { my $res = ''; $res |= $vectors[$_] for @{$AoA[0]}; int(@AoA) - unpack "%32b*", $res; }, regex1 => sub { my $omit = $AoA[0]; my $pat = '[^'.( join '', map quotemeta, pack 'C*', @$omit ).' +]{4}'; my $re = qr/\G(?:.{4})*?($pat)/s; int(() = $AoA =~ /$re/g); }, regex2 => sub { my $pat = qr/[$b[0]]/; my $cnt = 0; $cnt += !/$pat/ for @b; $cnt; }, };

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[ovedpo15]: another question about regex. if I have a string like this: "a/b/,c/d/e,5" I would like to remove the string after the last comma so the output will be "a/b/,c/d/e" how to do so?
[Corion]: ovedpo15: You could split on comma, and then join everything together, except the last part. Or you could match and make sure that the last part has no comma, like qr!,[^,]+$!, or you could use rindex.
[ovedpo15]: But I don't know the length of the string. will it still work?
[ovedpo15]: The only thing I know is that there is a comma at the end and a value after that
[hippo]: Try it and see. Your computer won't explode.
[Corion]: length will tell you the length of a string.

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