package Lingua::Stem::EnBroken;
# $RCSfile: En.pm,v $ $Revision: 1.4 $ $Date: 1999/06/24 23:33:37 $ $Author: snowhare $
=head1 NAME
Lingua::Stem::EnBroken - Porter's stemming algorithm for 'generic' English
=head1 SYNOPSIS
use Lingua::Stem::EnBroken;
my $stems = Lingua::Stem::EnBroken::stem({ -words => $word_list_reference,
-locale => 'en',
-exceptions => $exceptions_hash,
});
=head1 DESCRIPTION
This routine MIS-applies the Porter Stemming Algorithm to its parameters,
returning the stemmed words. It is an intentionally broken version
of Lingua::Stem::En for people needing backwards compatibility with
Lingua::Stem 0.30 and Lingua::Stem 0.40. Do not use it if you aren't
one of those people.
It is derived from the C program "stemmer.c"
as found in freewais and elsewhere, which contains these notes:
Purpose: Implementation of the Porter stemming algorithm documented
in: Porter, M.F., "An Algorithm For Suffix Stripping,"
Program 14 (3), July 1980, pp. 130-137.
Provenance: Written by B. Frakes and C. Cox, 1986.
I have re-interpreted areas that use Frakes and Cox's "WordSize"
function. My version may misbehave on short words starting with "y",
but I can't think of any examples.
The step numbers correspond to Frakes and Cox, and are probably in
Porter's article (which I've not seen).
Porter's algorithm still has rough spots (e.g current/currency, -ings words),
which I've not attempted to cure, although I have added
support for the British -ise suffix.
=head1 CHANGES
2003.09.28 - Documentation fix
2000.09.14 - Forked from the Lingua::Stem::En.pm module to provide
a backward compatibly broken version for people needing
consistent behavior with 0.30 and 0.40 more than accurate
stemming.
=cut
#######################################################################
# Initialization
#######################################################################
use strict;
use Exporter;
use Carp;
use vars qw (@ISA @EXPORT_OK @EXPORT %EXPORT_TAGS $VERSION);
BEGIN {
@ISA = qw (Exporter);
@EXPORT = ();
@EXPORT_OK = qw (stem clear_stem_cache stem_caching);
%EXPORT_TAGS = ();
}
$VERSION = "2.13";
my $Stem_Caching = 0;
my $Stem_Cache = {};
#
#V Porter.pm V2.11 25 Aug 2000 stemming cache
# Porter.pm V2.1 21 Jun 1999 with '&$sub if defined' not 'eval ""'
# Porter.pm V2.0 25 Nov 1994 (for Perl 5.000)
# porter.pl V1.0 10 Aug 1994 (for Perl 4.036)
# Jim Richardson, University of Sydney
# jimr@maths.usyd.edu.au or http://www.maths.usyd.edu.au:8000/jimr.html
# Find a canonical stem for a word, assumed to consist entirely of
# lower-case letters. The approach is from
#
# M. F. Porter, An algorithm for suffix stripping, Program (Automated
# Library and Information Systems) 14 (3) 130-7, July 1980.
#
# This algorithm is used by WAIS: for example, see freeWAIS-0.3 at
#
# http://kudzu.cnidr.org/cnidr_projects/cnidr_projects.html
# Some additional rules are used here, mainly to allow for British spellings
# like -ise. They are marked ** in the code.
# Initialization required before using subroutine stem:
# We count syllables slightly differently from Porter: we say the syllable
# count increases on each occurrence in the word of an adjacent pair
#
# [aeiouy][^aeiou]
#
# This avoids any need to define vowels and consonants, or confusion over
# 'y'. It also works slightly better: our definition gives two syllables
# in 'yttrium', while Porter's gives only one because the initial 'y' is
# taken to be a consonant. But it is not quite obvious: for example,
# consider 'mayfly' where, when working backwards (see below), the 'yf'
# matches the above pattern, even though it is the 'ay' which in Porter's
# terms increments the syllable count.
#
# We wish to match the above in context, working backwards from the end of
# the word: the appropriate regular expression is
my $syl = '[aeiou]*[^aeiou][^aeiouy]*[aeiouy]';
# (This works because [^aeiouy] is a subset of [^aeiou].) If we want two
# syllables ("m>1" in Porter's terminology) we can just match $syl$syl.
# For step 1b we need to be able to detect the presence of a vowel: here
# we revert to Porter's definition that a vowel is [aeiou], or y preceded
# by a consonant. (If the . below is a vowel, then the . is the desired
# vowel; if the . is a consonant the y is the desired vowel.)
my $hasvow = '[^aeiouy]*([aeiou]|y.)';
=head1 METHODS
=cut
#######################################################################
=over 4
=item stem({ -words => \@words, -locale => 'en', -exceptions => \%exceptions });
Stems a list of passed words using the rules of US English. Returns
an anonymous array reference to the stemmed words.
Example:
my $stemmed_words = Lingua::Stem::EnBroken::stem({ -words => \@words,
-locale => 'en',
-exceptions => \%exceptions,
});
=back
=cut
sub stem {
return [] if ($#_ == -1);
my $parm_ref;
if (ref $_[0]) {
$parm_ref = shift;
} else {
$parm_ref = { @_ };
}
my $words = [];
my $locale = 'en';
my $exceptions = {};
foreach (keys %$parm_ref) {
my $key = lc ($_);
if ($key eq '-words') {
@$words = @{$parm_ref->{$key}};
} elsif ($key eq '-exceptions') {
$exceptions = $parm_ref->{$key};
} elsif ($key eq '-locale') {
$locale = $parm_ref->{$key};
} else {
croak (__PACKAGE__ . "::stem() - Unknown parameter '$key' with value '$parm_ref->{$key}'\n");
}
}
local( $_ );
foreach (@$words) {
# Flatten case
$_ = lc $_;
# Check against exceptions list
if (exists $exceptions->{$_}) {
$_ = $exceptions->{$_};
next;
}
# Check against cache of stemmed words
my $original_word = $_;
if ($Stem_Caching && exists $Stem_Cache->{$original_word}) {
$_ = $Stem_Cache->{$original_word};
next;
}
# Step 0 - remove punctuation
s/'s$//; s/^[^a-z]+//; s/[^a-z]+$//;
next unless /^[a-z]+$/;
# Reverse the word so we can easily apply pattern matching to the end:
$_ = reverse $_;
# Step 1a: plurals -- sses->ss, ies->i, ss->ss, s->0
m!^s! && ( s!^se(ss|i)!$1! || s!^s([^s])!$1! );
# Step 1b: participles -- SYLeed->SYLee, VOWed->VOW, VOWing->VOW;
# but ated->ate etc
s!^dee($syl)!ee$1!o ||
(
s!^(de|gni)($hasvow)!$2!o &&
(
# at->ate, bl->ble, iz->ize, is->ise
s!^(ta|lb|[sz]i)!e$1! || # ** ise as well as ize
# CC->C (C consonant other than l, s, z)
s!^([^aeioulsz])\1!$1! ||
# (m=1) CVD->CVDe (C consonant, V vowel, D consonant not w, x, y)
s!^([^aeiouwxy][aeiouy][^aeiou]+)$!e$1!
)
);
# Step 1c: change y to i: happy->happi, sky->sky
s!^y($hasvow)!i$1!o;
# Step 2: double and triple suffices (part 1)
# Switch on last three letters (fails harmlessly if subroutine undefined) --
# thanks to Ian Phillipps <ian@dial.pipex.com> who wrote
# CPAN authors/id/IANPX/Stem-0.1.tar.gz
# for suggesting the replacement of
# eval( '&S2' . unpack( 'a3', $_ ) );
# (where the eval ignores undefined subroutines) by the much faster
# eval { &{ 'S2' . substr( $_, 0, 3 ) } };
# But the following is slightly faster still:
my $sub;
&$sub if defined &{ $sub = 'S2' . substr( $_, 0, 3 ) };
# Step 3: double and triple suffices, etc (part 2)
&$sub if defined &{ $sub = 'S3' . substr( $_, 0, 3 ) };
# Step 4: single suffices on polysyllables
&$sub if defined &{ $sub = 'S4' . substr( $_, 0, 2 ) };
# Step 5a: tidy up final e -- probate->probat, rate->rate; cease->ceas
m!^e! && ( s!^e($syl$syl)!$1!o ||
# Porter's ( m=1 and not *o ) E where o = cvd with d a consonant
# not w, x or y:
! m!^e[^aeiouwxy][aeiouy][^aeiou]! && # not *o E
s!^e($syl[aeiouy]*[^aeiou]*)$!$1!o # m=1
);
# Step 5b: double l -- controll->control, roll->roll
# ** Note correction: Porter has m>1 here ($syl$syl), but it seems m>0
# ($syl) is wanted to strip an l off controll.
s!^ll($syl)!l$1!o;
$_ = scalar( reverse $_ );
$Stem_Cache->{$original_word} = $_ if $Stem_Caching;
}
$Stem_Cache = {} if ($Stem_Caching < 2);
return $words;
}
##############################################################
=over 4
=item stem_caching({ -level => 0|1|2 });
Sets the level of stem caching.
'0' means 'no caching'. This is the default level.
'1' means 'cache per run'. This caches stemming results during a single
call to 'stem'.
'2' means 'cache indefinitely'. This caches stemming results until
either the process exits or the 'clear_stem_cache' method is called.
=back
=cut
sub stem_caching {
my $parm_ref;
if (ref $_[0]) {
$parm_ref = shift;
} else {
$parm_ref = { @_ };
}
my $caching_level = $parm_ref->{-level};
if (defined $caching_level) {
if ($caching_level !~ m/^[012]$/) {
croak(__PACKAGE__ . "::stem_caching() - Legal values are '0','1' or '2'. '$caching_level' is not a legal value");
}
$Stem_Caching = $caching_level;
}
return $Stem_Caching;
}
##############################################################
=over 4
=item clear_stem_cache;
Clears the cache of stemmed words
=back
=cut
sub clear_stem_cache {
$Stem_Cache = {};
}
##############################################################
=head1 NOTES
This code is almost entirely derived from the Porter 2.1 module
written by Jim Richardson.
=head1 SEE ALSO
Lingua::Stem
=head1 AUTHOR
Jim Richardson, University of Sydney
jimr@maths.usyd.edu.au or http://www.maths.usyd.edu.au:8000/jimr.html
Integration in Lingua::Stem by
Benjamin Franz, FreeRun Technologies,
snowhare@nihongo.org or http://www.nihongo.org/snowhare/
=head1 COPYRIGHT
Jim Richardson, University of Sydney
Benjamin Franz, FreeRun Technologies
This code is freely available under the same terms as Perl.
=head1 BUGS
=head1 TODO
=cut
1;