number of matches

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

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Re: number of matches by BrowserUk (Patriarch) on Sep 02, 2004 at 21:55 UTC
`my $s = 'the quick brown fox jumps over the lazy dog'; my $vowels = () = $s =~ m[[aeiou]]g; print "There are $vowels vowels in '$s'"; There are 11 vowels in 'the quick brown fox jumps over the lazy dog'` [download] Examine what is said, not who speaks. "Efficiency is intelligent laziness." -David Dunham "Think for yourself!" - Abigail "Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon	[reply] [d/l]
Re: number of matches by wufnik (Friar) on Sep 02, 2004 at 21:53 UTC
i am presuming you do not want overlapping matches; ie you want simple repeat detection: if this is the case something like: `my $searchstring = 'humptydumpty'; my @matches = $searchstring =~ /umpty/g;` [download] should work, leaving you able to access the number of matches by using scalar @matches or whatever ...wufnik -- in the world of the mules there are no rules --	[reply] [d/l]
Re: number of matches by bobf (Monsignor) on Sep 02, 2004 at 22:01 UTC
If you are counting characters, you can use tr//. If you are matching strings, you can use s//. Both return the number of substitutions made: `$count = ($line =~ tr/X/X/); $count = ($line =~ s/(match1\|match2)/$1/g);` [download] Just make sure you reset the position with the pos function if you are using a string (vs a single character) and you want to find overlapping matches. HTH	[reply] [d/l]
Re^2: number of matches by Rhandom (Curate) on Sep 03, 2004 at 14:49 UTC
Didn't benchmark - but I believe tr/X/X/ is still modifying the string on the backend (unless there is some unknown optimization). It is better to leave off the second X as in tr/X//. This will not attempt to modify the string and will still return the count - as in: `perl -e '$a="aaa"; $i=$a=~tr/a//; print "($i)($a)\n";'` [download] my @a=qw(random brilliant braindead); print $a[rand(@a)];	[reply] [d/l]
Re: number of matches by Anonymous Monk on Sep 03, 2004 at 09:16 UTC
`$count = () = $str =~ /PATTERN/g; # Non-overlapping mat +ches $count = () = $str =~ /(?=(PATTERN))/g; # Overlapping matches $count = 0; $str =~ /PATTERN(?{$count ++})(?!)/; # All matches` [download]	[reply] [d/l]
Re: number of matches by frank_2k4 (Acolyte) on Sep 02, 2004 at 21:57 UTC
You could use a counter `counter = 0; @regex = qw( reg ex patterns ); for (@regex){ if (/\Q$_\E/){ $counter ++' } } print $counter;` [download]	[reply] [d/l]
Re: number of matches by Anonymous Monk on Sep 03, 2004 at 18:58 UTC
`$count=scalar(my @dummy = $string=~m/$regex/g);` [download] will count the matches. If you don't assign the pattern match to an array, m//g will interpret this as a scalar context and only return the first occurrence, and the scalar function will then return 1.	[reply] [d/l]