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Optimizing many many regex matches

by BUU (Prior)
on Oct 22, 2006 at 19:49 UTC ( #579894=perlquestion: print w/replies, xml ) Need Help??

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

I've recently come upon a mildly interesting problem without much immediate relevance, so I've been considering it but I haven't gotten around to solving it. The situation is fairly simple, I have a list of around 40 to 100+ objects. Each object contains a 'regexp' value and a 'code' value. The idea is to execute each 'code' value that has its corresponding regexp match. Now, the obvious and simple way I've been using looks like this:
my $string; for( @regexes ) { if( @matches = $string =~ $_->{regexp} ) { $_->{code}->($string, @matches); } }
But this strikes me as slightly inefficient in a number of ways. Surely the regexp engine could optimize this if only it knew about all the matches I was intending to perform. There are a number of modules on CPAN that advertising combining lots of regexp to do a simple boolean check, but I couldn't see an easy way to then match this back to the appropiate 'code' value that's also in the datastructure. Also, each regexp might have one or more capturing fields I need to keep track of and pass to the code ref. Any thoughts?

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Re: Optimizing many many regex matches
by grinder (Bishop) on Oct 22, 2006 at 20:16 UTC

    BUU, what you want is Regexp::Assemble, and create a pattern in "tracked" mode. This will allow you to assemble a single pattern against which to test strings. Big efficiency gain there.

    You can then recover the original pattern that triggered the match, use that as a key into a dispatch table, passing in the captured fields. Have a look at eg/ircwatcher to get some ideas. A more advanced version appeared in Perl Hacks, if you happen to have a copy lying around.

    • another intruder with the mooring in the heart of the Perl

Re: Optimizing many many regex matches
by xdg (Monsignor) on Oct 22, 2006 at 22:25 UTC

    This might be a situation where study might be helpful. Here's section from the docs:

    Takes extra time to study SCALAR ($_ if unspecified) in anticipation +of doing many pattern matches on the string before it is next modifie +d. This may or may not save time, depending on the nature and number +of patterns you are searching on, and on the distribution of characte +r frequencies in the string to be searched--you probably want to comp +are run times with and without it to see which runs faster. Those loo +ps that scan for many short constant strings (including the constant +parts of more complex patterns) will benefit most.


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