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.