Provided by: liblingua-stem-snowball-perl_0.952-3build2_amd64 
NAME
Lingua::Stem::Snowball - Perl interface to Snowball stemmers.
SYNOPSIS
my @words = qw( horse hooves );
# OO interface:
my $stemmer = Lingua::Stem::Snowball->new( lang => 'en' );
$stemmer->stem_in_place( \@words ); # qw( hors hoov )
# Functional interface:
my @stems = stem( 'en', \@words );
DESCRIPTION
Stemming reduces related words to a common root form -- for instance, "horse", "horses",
and "horsing" all become "hors". Most commonly, stemming is deployed as part of a search
application, allowing searches for a given term to match documents which contain other
forms of that term.
This module is very similar to Lingua::Stem -- however, Lingua::Stem is pure Perl, while
Lingua::Stem::Snowball is an XS module which provides a Perl interface to the C version of
the Snowball stemmers. (<http://snowball.tartarus.org>).
Supported Languages
The following stemmers are available (as of Lingua::Stem::Snowball 0.95):
|-----------------------------------------------------------|
| Language | ISO code | default encoding | also available |
|-----------------------------------------------------------|
| Danish | da | ISO-8859-1 | UTF-8 |
| Dutch | nl | ISO-8859-1 | UTF-8 |
| English | en | ISO-8859-1 | UTF-8 |
| Finnish | fi | ISO-8859-1 | UTF-8 |
| French | fr | ISO-8859-1 | UTF-8 |
| German | de | ISO-8859-1 | UTF-8 |
| Hungarian | hu | ISO-8859-1 | UTF-8 |
| Italian | it | ISO-8859-1 | UTF-8 |
| Norwegian | no | ISO-8859-1 | UTF-8 |
| Portuguese | pt | ISO-8859-1 | UTF-8 |
| Romanian | ro | ISO-8859-2 | UTF-8 |
| Russian | ru | KOI8-R | UTF-8 |
| Spanish | es | ISO-8859-1 | UTF-8 |
| Swedish | sv | ISO-8859-1 | UTF-8 |
| Turkish | tr | UTF-8 | |
|-----------------------------------------------------------|
Benchmarks
Here is a comparison of Lingua::Stem::Snowball and Lingua::Stem, using The Works of Edgar
Allen Poe, volumes 1-5 (via Project Gutenberg) as source material. It was produced on a
3.2GHz Pentium 4 running FreeBSD 5.3 and Perl 5.8.7. (The benchmarking script is included
in this distribution: devel/benchmark_stemmers.plx.)
|--------------------------------------------------------------------|
| total words: 454285 | unique words: 22748 |
|--------------------------------------------------------------------|
| module | config | avg secs | rate |
|--------------------------------------------------------------------|
| Lingua::Stem 0.81 | no cache | 2.029 | 223881 |
| Lingua::Stem 0.81 | cache level 2 | 1.280 | 355025 |
| Lingua::Stem::Snowball 0.94 | stem | 1.426 | 318636 |
| Lingua::Stem::Snowball 0.94 | stem_in_place | 0.641 | 708495 |
|--------------------------------------------------------------------|
METHODS / FUNCTIONS
new
my $stemmer = Lingua::Stem::Snowball->new(
lang => 'es',
encoding => 'UTF-8',
);
die $@ if $@;
Create a Lingua::Stem::Snowball object. new() accepts the following hash style
parameters:
• lang: An ISO code taken from the table of supported languages, above.
• encoding: A supported character encoding.
Be careful with the values you supply to new(). If "lang" is invalid,
Lingua::Stem::Snowball does not throw an exception, but instead sets $@. Also, if you
supply an invalid combination of values for "lang" and "encoding", Lingua::Stem::Snowball
will not warn you, but the behavior will change: stem() will always return undef, and
stem_in_place() will be a no-op.
stem
@stemmed = $stemmer->stem( WORDS, [IS_STEMMED] );
@stemmed = stem( ISO_CODE, WORDS, [LOCALE], [IS_STEMMED] );
Return lowercased and stemmed output. WORDS may be either an array of words or a single
scalar word.
In a scalar context, stem() returns the first item in the array of stems:
$stem = $stemmer->stem($word);
$first_stem = $stemmer->stem(\@words); # probably wrong
LOCALE has no effect; it is only there as a placeholder for backwards compatibility (see
Changes). IS_STEMMED must be a reference to a scalar; if it is supplied, it will be set
to 1 if the output differs from the input in some way, 0 otherwise.
stem_in_place
$stemmer->stem_in_place(\@words);
This is a high-performance, streamlined version of stem() (in fact, stem() calls
stem_in_place() internally). It has no return value, instead modifying each item in an
existing array of words. The words must already be in lower case.
lang
my $lang = $stemmer->lang;
$stemmer->lang($iso_language_code);
Accessor/mutator for the lang parameter. If there is no stemmer for the supplied ISO code,
the language is not changed (but $@ is set).
encoding
my $encoding = $stemmer->encoding;
$stemmer->encoding($encoding);
Accessor/mutator for the encoding parameter.
stemmers
my @iso_codes = stemmers();
my @iso_codes = $stemmer->stemmers();
Returns a list of all valid language codes.
REQUESTS & BUGS
Please report any requests, suggestions or bugs via the RT bug-tracking system at
http://rt.cpan.org/ or email to bug-Lingua-Stem-Snowball@rt.cpan.org.
http://rt.cpan.org/NoAuth/Bugs.html?Dist=Lingua-Stem-Snowball is the RT queue for
Lingua::Stem::Snowball. Please check to see if your bug has already been reported.
AUTHORS
Lingua::Stem::Snowball was originally developed to provide access to stemming algorithms
for the OpenFTS (full text search engine) project (<http://openfts.sourceforge.net>), by
Oleg Bartunov, <oleg at sai dot msu dot su> and Teodor Sigaev, <teodor at stack dot net>.
Currently maintained by Marvin Humphrey <marvin at rectangular dot com>. Previously
maintained by Fabien Potencier <fabpot at cpan dot org>.
COPYRIGHT AND LICENSE
Perl bindings copyright 2004-2008 by Marvin Humphrey, Fabien Potencier, Oleg Bartunov and
Teodor Sigaev.
This software may be freely copied and distributed under the same terms and conditions as
Perl.
Snowball files and stemmers are covered by the BSD license.
SEE ALSO
<http://snowball.tartarus.org>, Lingua::Stem.