most terse regex match count

bliako has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: most terse regex match count by haukex (Archbishop) on May 16, 2019 at 15:32 UTC
Is it possible to force list context in a conditional? A variation of the "Saturn" operator does the trick: `if ( 2 == ( () = $outs =~ m\|A\|gs ) )`	[reply] [d/l]
Re^2: most terse regex match count by Veltro (Hermit) on May 17, 2019 at 14:38 UTC
Quick thought to reduce capturing: `m\|()A\|gs`? If I understand docu correctly the list is populated and then the values are discarded. So collect the smallest possible value instead.	[reply] [d/l]
Re^3: most terse regex match count by haukex (Archbishop) on May 18, 2019 at 19:13 UTC
Quick thought to reduce capturing: `m\|()A\|gs`? Unfortunately it seems the extra capture group actually slows things down - no matter how much I fiddle with the parameters at the top, `nocapt` is always about 2x as fast: `#!/usr/bin/env perl use warnings; use strict; use Benchmark qw/cmpthese/; my $count = 1000; my $match = 'ABC'x20; my $space = 'xAz'x100; my $str = ( $space.$match x $count ) . $space; cmpthese(-3, { nocapt => sub { die unless $count == ( () = $str =~ m\|\Q$match\|gs ); }, withcapt => sub { die unless $count == ( () = $str =~ m\|()\Q$match\|gs ); }, }); __END__ Rate withcapt nocapt withcapt 4264/s -- -50% nocapt 8596/s 102% --` [download]	[reply] [d/l] [select]
Re: most terse regex match count by Fletch (Bishop) on May 16, 2019 at 15:32 UTC
You want 3/4ths of the operator which shall not be named and some extra parens. `if( 2 == ( ()= $outs =~ m\|A\|gs ) ){ print "exactly 2 matches\n" }` [download] The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l]
Re: most terse regex match count by jwkrahn (Abbot) on May 16, 2019 at 19:09 UTC
`$ perl -le'my $x = "A B C\nA B D\n"; print "exactly two matches" if $x + =~ /^ [^A]* A [^A]* A [^A]* $/xg' exactly two matches` [download]	[reply] [d/l]
Re: most terse regex match count by holli (Abbot) on May 17, 2019 at 09:30 UTC
`map` gets abused so often, it can take another hit: `if ( 2 == map $_, $outs =~ m\|A\|gs )` [download] Or maybe it's no abuse. Could be a plain `map $_,` construct gets optimized by perl somehow? holli You can lead your users to water, but alas, you cannot drown them.	[reply] [d/l] [select]
Re^2: most terse regex match count by hippo (Bishop) on May 17, 2019 at 09:52 UTC
Could be a plain `map $_,` construct gets o******* by perl somehow?* SHH! Don't use the o-word here or people will start posting benchmarks. ;-)	[reply] [d/l]
Re: most terse regex match count by Marshall (Canon) on May 17, 2019 at 05:49 UTC
Yes, it is possible to achieve your stated objective, although that is not perhaps the best way to code what you are doing. Be aware that "terse" does not necessarily mean faster code. Perhaps, one way: `#!/usr/bin/perl use strict; use warnings; my $outs = <<'EOS'; A B C A B D A D E EOS print $outs; my %hash; foreach (split ' ',$outs) { $hash{$_}++; } print "Values occurring exactly twice:\n"; foreach (keys %hash) { print "$_\n" if ($hash{$_} ==2); } __END__ A B C A B D A D E Values occurring exactly twice: B D` [download] Another way: `#!/usr/bin/perl use strict; use warnings; my $outs = <<'EOS'; A B C A B D A D E EOS if ( (()=$outs =~ m\|D\|g)==2) { print "exactly 2 matches for D\n" } # I think better written as: my @matches = $outs =~ m\|D\|g; print "exactly 2 matches for D\n" if @matches ==2;` [download] Update: Without running deparse, I figure that `()=$outs =~ m\|D\|g` is going to create an internal array similar to @matches, it just won't have a name in the source code. I like the 2 line version because I don't blind the reader with parens and it is both a) very easy to understand and b) will run just as quickly as the one line version. Do not mistake "terse" for "speed". It can even happen that terse is slower. Of course, if just looking for a single letter, tr is the fastest: `if ( $outs =~ tr/D// == 2) { print "exactly 2 matches for D\n" }` [download]	[reply] [d/l] [select]
Re^2: most terse regex match count by holli (Abbot) on May 17, 2019 at 09:39 UTC
Be aware that "terse" does not necessarily mean f**** code.* SHH! Don't use the f-word here or people will start posting benchmarks. holli You can lead your users to water, but alas, you cannot drown them.	[reply]
Re^2: most terse regex match count by bliako (Monsignor) on May 17, 2019 at 10:17 UTC
Be aware that "terse" does not necessarily mean faster code. Sure, I was just trying to show off to the future generations looking at the test file. `tr` is an interesting idea but I need to find longer strings.	[reply] [d/l]
Re: most terse regex match count by bliako (Monsignor) on May 16, 2019 at 15:51 UTC
thanks! A part of Perl I have avoided so far. Saturn reminded me of mooning	[reply]
Re^2: most terse regex match count by LanX (Saint) on May 16, 2019 at 15:56 UTC
> Saturn reminded me of mooning FYI Poll: How should the =( )= be called??? =) Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply]
Re^3: most terse regex match count by bliako (Monsignor) on May 16, 2019 at 16:15 UTC
beats SO any and every day	[reply]


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