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Re: split question

by Anonymous Monk
on Sep 20, 2002 at 12:58 UTC ( [id://199451]=note: print w/replies, xml ) Need Help??


in reply to split question

Nevermind, I found my answer in:

$var =~ m/.+\:(.+?)\s.+\:(.+?)\s.+\:(.+?)/;

Replies are listed 'Best First'.
Re: Re: split question
by RMGir (Prior) on Sep 20, 2002 at 13:20 UTC
    Greed is bad. More specifically, greedy quantifiers for some regexes are bad; they can slow things down.

    I compared your regex (called greedy) with a version using the +? nongreedy qualifier, both against your string (where both will give correct results) and a much longer string, where the non-greedy version will match the first 3 codes, and the greedy version will match the first code and the last 2.

    $ perl testGreed.pl Benchmark: running greedyLong, greedyShort, notGreedyLong, notGreedySh +ort, each for at least 3 CPU seconds... greedyLong: 3 wallclock secs ( 3.00 usr + 0.00 sys = 3.00 CPU) @ 42 +264.23/s (n=127004) greedyShort: 4 wallclock secs ( 3.20 usr + 0.01 sys = 3.21 CPU) @ 8 +8692.45/s (n=284348) notGreedyLong: 4 wallclock secs ( 3.13 usr + 0.01 sys = 3.14 CPU) @ + 46018.76/s (n=144729) notGreedyShort: 3 wallclock secs ( 2.99 usr + 0.01 sys = 3.00 CPU) +@ 101593.68/s (n=305289) Rate greedyLong notGreedyLong greedyShort notG +reedyShort greedyLong 42264/s -- -8% -52% + -58% notGreedyLong 46019/s 9% -- -48% + -55% greedyShort 88692/s 110% 93% -- + -13% notGreedyShort 101594/s 140% 121% 15% + --
    As you can see, the non-greedy version runs considerably faster, since it doesn't wind up trying as many alternatives (a.k.a. backtracking).

    Here's the comparison code:

    Those results were with 5.6.1 on Cygwin, your results may vary.
    --
    Mike
Re: Re: split question
by sauoq (Abbot) on Sep 20, 2002 at 20:31 UTC

    One way to do it with split:

    #!/usr/bin/perl -w use strict; my $var = "xxx:12345 yyy:54321 zzz:13245"; my @items = split /:\S+\s*/, $var; print"@items\n"; __END__ xxx yyy zzz
    -sauoq
    "My two cents aren't worth a dime.";
    

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