[prev in list] [next in list] [prev in thread] [next in thread]
List: perl5-porters
Subject: Regexp::Optimizer 0.01 released
From: Dan Kogai <dankogai () dan ! co ! jp>
Date: 2003-05-31 11:25:06
[Download RAW message or body]
Porters,
perltodo says
> Factoring out common suffices/prefices in regexps (trie optimization)
>
> Currently, the user has to optimize "foo|far" and "foo|goo" into
> "f(?:oo|ar)" and "[fg]oo" by hand; this could be done
> automatically.
I have written a module that attempts to do this as Regexp::Optimizer
as follows
http://www.dan.co.jp/~dankogai/Regexp-Optimizer-0.01.tar.gz
Also uploaded to CPAN.
It comes with two modules. Regexp::Optimizer is a frontend which
actually takes regular expression and optimize it (even with nested
group). Which is implemented as a inherited class of Regex::List which
offers list2re() that converts list of words into a trie-optimized
regular expression.
Though Regexp::Optimizer is still rather rudimentary, Regex::List is
pretty robust. I will attach pod2text'ed Regexp::List right after my
signature.
* Unlike Regex::Presuf, it applies prefix aggregation only to leaf
nodes of the trie so it is much faster -- fast enough to turn every
word in /usr/share/dict/words into an optimized regexp (2 minutes on my
FreeBSD box).
* Another difference from Regex::Presuf is that the order is
"respected". Order is in fact preserved unless there is no "?" and
character class aggregation. I made it that way because I needed to
use it for a list of regular expressions, not just words. When it
comes to group alterations, order does matter ( qr/fooo|fo/ is
DIFFERENT from qr/fo|fooo/).
Comments very welcome.
Enjoy!
Dan the Perl5 Porter
====================
NAME
Regexp::List - builds regular expressions out of a list of words
SYNOPSIS
use Regexp::List;
my $l = Regexp::List->new;
my $re = $l->list2re(qw/foobar fooxar foozap/);
# $re is now qr/foo(?:[bx]ar|zap)/
ABSTRACT
This module offers "list2re" method that turns a list of words into
an
optimized regular expression which matches all words therein.
The optimized regular expression is much more efficient than a
simple-minded '|'-concatenation thereof.
DESCRIPTION
This module use Object-Oriented approach so you can use this module
as a
base and tweak its features. This module is a base class of
Regexp::Optimizer.
EXPORT
Since this is an OO module there is no symbol exported.
METHODS
This module offers methods below;
$l = Regexp::List->new(*key=>value, ...*)
Constructor. When arguments are fed in *key => value,* manner,
it
sets attributes. See "$l->set" for details
$re = $l->list2re(*list of words ...*)
Does the job. Takes a list of words and turn it into an optimal
regular expresson. See "IMPLEMENTATION" to find out how it is
achieved. If you want to know the underlying black magic even
further, see the source.
$l->set(*key=>value, ...*)
Sets attributes. There are many attributes supported but let me
mention just a few that you may be interested.
lookahead
Whether you prepend a lookahead assertion or not. Default
value
is 1. This module is smart enough to omit the assertion
when you
don't need one.
$re = $l->list2re(qw/1 2 3 infinity/);
# qr/(?=[123i])(?:[123]|infinity)/
$re = $l->set(lookahead=>0)->list2re(qw/1 2 3 infinity/);
# qr/(?:[123]|infinity)/
quotemeta
Whether you quote metacharacters or not. Default is 1. If
you
really need this feature try Regexp::Optimizer instead.
@list = qw/3 3.14 3.14159265358979/;
$re = $l->list2re(@list);
# qr/3(?:\.14(?:159265358979)?)?)/
$re = $l->set(lookahead=>0)->list2re(@list);
# qr/3(?:.14(?:159265358979)?)?)/
# which does match 3.14 but also "11+3=14"
modifies
Currently it accepts 'i', 'm', 's', and 'x', the same as
regular
expression modifiers.
@list = qw/Perl perl BASIC basic/;
$re = $l->list2re(@list);
# qr/(?=[BPbp])(?:[Pp]erl|BASIC|basic)/
$re = $l->set(modifiers => 'i')->list2re(@list);
# qr/(?=[bp])(?:perl|basic)/i
print $l->set(modifiers => 'x')->list2re(@list);
# Try for yourself; Isn't it cute ?
$l->expand($re);
Utility methods to expand a regular expression. Handy when you
want
to check the complex regexes.
$l->unexpand($re);
Utility methods to unexpand a regular expression.
IMPLEMENTATION
This module optimizes the regular expression as follows. Let's see
what
happens when qw/foobar fooxar foozap fooza/ is fed
trie building (common prefix aggregation)
first the corresponding *trie* structure is built
+- bar
foo -+- xar
+- za -+- p
+- ''
common suffix aggregation
it checks if any leaf node can be optimized for common suffix.
In
this case we can do so to "bar" and "xar".
+- b -+-ar
foo -+- x -+
+- za -+- p
+- ''
character class conversion
If a branch contains more than two single characters, it turns
it
into a character class.
foo -+- [bx] --- ar
+- za -+-p
+- ''
empty leaf to "?"
Empty leaf is converted to a '?' quantifier
foo -+- [bx] --- ar
+- za -+-p?
join all leafs into a group
And the final result is reached.
foo(?:[bx]ar|zap?)
BENCHMARKS
This module is faily robust. You can practically use this module to
find
a regular expression that matches all words in a dictionary. Here
is a
result by on perl 5.8.0, FreeBSD 4-Stable, Pentium III 800 Mhz with
512
MB RAM.
# Sat May 31 09:11:06 2003 ( 0.000000 s) Reading
/usr/share/dict/words
# Sat May 31 09:11:07 2003 ( 0.847797 s) 235881 lines read.
# Sat May 31 09:11:07 2003 ( 0.000000 s) Making regexp.
# Sat May 31 09:13:09 2003 ( 121.596928 s) Done.
# Sat May 31 09:13:09 2003 ( 0.000000 s) Saving to t/words.rx
# Sat May 31 09:13:09 2003 ( 0.000000 s) Reading t/words.rx
# Sat May 31 09:13:13 2003 ( 3.679176 s) Done.
# Sat May 31 09:13:13 2003 ( 0.000000 s) Opening
/usr/share/dict/words for comparison.
# Sat May 31 09:13:13 2003 ( 0.255222 s)
/usr/share/dict/words:235881 lines found.
# Sat May 31 09:13:13 2003 ( 0.000000 s) Showtime!
# 235881/235881
# Sat May 31 10:44:17 2003 ( 5464.370409 s) Done.
# Sat May 31 10:44:17 2003 ( 5464.370624 s) 43.167 matches/s
The result of optimization is obvious as the number of alteration
increases. Here is a result of a benchmark which matches randomly
picked
words against "/usr/share/dict/words".
==== 2 words
Rate naive optim
naive 1.79/s -- -28%
optim 2.49/s 39% --
==== 256 words
s/iter naive optim
naive 31.7 -- -81%
optim 5.95 433% --
SEE ALSO
Regexp::Optimizer -- uses this module as its base
"eg/" directory in this package contains example scripts.
Perl standard documents
L<perltodo>, L<perlre>
CPAN Modules
Regexp::Presuf, Text::Trie
Books
Mastering Regular Expressions
<http://www.oreilly.com/catalog/regex2/>
AUTHOR
Dan Kogai <dankogai@dan.co.jp>
COPYRIGHT AND LICENSE
Copyright 2003 by Dan Kogai, All Rights Reserved.
This library is free software; you can redistribute it and/or
modify it
under the same terms as Perl itself.
dankogai@dan-attic[4705]:~/work/Regexp-Optimizer>
[prev in list] [next in list] [prev in thread] [next in thread]
Configure |
About |
News |
Add a list |
Sponsored by KoreLogic