Re: You don't always have to use regexes

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Re^2: You don't always have to use regexes by kvale (Monsignor) on Feb 23, 2005 at 16:32 UTC
I think that for the index case the situation is not so clear. Both the regex engine and index() will use the same Boyer-Moore routine and for me personally, the regex version is more readable. But as always, YMMV. `use Benchmark qw(:all) ; my $value = 'FALSE'; my $count = 1_000_000; cmpthese($count, { 'regex' => sub { $value =~ /^true$/i }, 'eq' => sub { lc $value eq "true" }, 'index' => sub { index( lc $value, "true" ) >= 0 }, });` [download] yields `Benchmark: timing 1000000 iterations of eq, index, regex... eq: 1 wallclock secs ( 0.89 usr + 0.00 sys = 0.89 CPU) @ 11 +23595.51/s (n=1000000) index: 2 wallclock secs ( 1.65 usr + 0.00 sys = 1.65 CPU) @ 60 +6060.61/s (n=1000000) regex: 2 wallclock secs ( 1.63 usr + 0.00 sys = 1.63 CPU) @ 61 +3496.93/s (n=1000000) Rate index regex eq index 606061/s -- -1% -46% regex 613497/s 1% -- -45% eq 1123596/s 85% 83% --` [download] Update: As AM has pointed out (thank you!), the benchmark above has a bug. Using the tests `'regex' => sub { $value =~ /true/i }, 'regex_anch' => sub { $value =~ /^true$/i }, 'eq' => sub { lc $value eq "true" }, 'index' => sub { index( lc $value, "true" ) >= 0 },` [download] I get the results Benchmark: timing 1000000 iterations of eq, index, regex, regex_anch.. +. eq: 1 wallclock secs ( 0.88 usr + 0.00 sys = 0.88 CPU) @ 11 +36363.64/s (n=1000000) index: 0 wallclock secs ( 1.65 usr + 0.00 sys = 1.65 CPU) @ 60 +6060.61/s (n=1000000) regex: 0 wallclock secs ( 1.08 usr + 0.00 sys = 1.08 CPU) @ 92 +5925.93/s (n=1000000) regex_anch: 2 wallclock secs ( 1.59 usr + 0.00 sys = 1.59 CPU) @ 62 +8930.82/s (n=1000000) Rate index regex_anch regex eq index 606061/s -- -4% -35% -47% regex_anch 628931/s 4% -- -32% -45% regex 925926/s 53% 47% -- -19% eq 1136364/s 87% 81% 23% -- [download] with the surprising result that the regex w/o the anchor is faster than the anchored version. Multiple runs yield similar results. As the AM says, one could try many different regex-value combos, but I expect the results to be not far different, precisely because both index and regex engine use the same BM function. -Mark	[reply] [d/l] [select]
Re^3: You don't always have to use regexes by Anonymous Monk on Feb 24, 2005 at 02:59 UTC
You Benchmark is significantly flawed for the question asked. The OR (original replier) wanted to compare `index(lc $value,"true")` with `$value =~ /true/i;` In addition, to fairly benchmark one should try multiple test case (set `$value` to "true", a short string, and a longer string in your test, and in a fair test, set it to: 'true', 'ashortstringthentrue', 'averylongstringthentrue', and different size strings without 'true' in them.	[reply] [d/l] [select]
Re^2: You don't always have to use regexes by holli (Abbot) on Feb 23, 2005 at 16:39 UTC
I benchmarked this and it yields an interesting result. `index()` is (a bit) faster than a regex. If it´s used in combination with `lc()`, as in your example, the regex with the i-modifier is faster. use strict; use warnings; use Benchmark; my $value = "somewhere here true is there!"; timethese ( 9000000, { 'index' => sub { index( $value, "true" ) }, 'regex' => sub { $value =~ /true/ }, } ); timethese ( 9000000, { 'index' => sub { index( lc $value, "true" ) }, 'regex' => sub { $value =~ /true/i }, } ); Benchmark: timing 9000000 iterations of index, regex... index: 2 wallclock secs ( 2.02 usr + 0.00 sys = 2.02 CPU) @ 44 +46640.32/s (n=9000000) regex: 4 wallclock secs ( 2.40 usr + -0.01 sys = 2.39 CPU) @ 37 +60969.49/s (n=9000000) Benchmark: timing 9000000 iterations of index, regex... index: 4 wallclock secs ( 4.55 usr + 0.00 sys = 4.55 CPU) @ 19 +79762.43/s (n=9000000) regex: 3 wallclock secs ( 3.68 usr + 0.00 sys = 3.68 CPU) @ 24 +48313.38/s (n=9000000) [download] Update: Ack. I really need to learn to type faster. holli, /regexed monk/	[reply] [d/l] [select]