NAME
Lingua::Stem::Any - Unified interface to any stemmer on CPAN
VERSION
This document describes Lingua::Stem::Any v0.04.
SYNOPSIS
use Lingua::Stem::Any;
# create German stemmer using the default source module
$stemmer = Lingua::Stem::Any->new(language => 'de');
# create German stemmer explicitly using Lingua::Stem::Snowball
$stemmer = Lingua::Stem::Any->new(
language => 'de',
source => 'Lingua::Stem::Snowball',
);
# get stem for word
$stem = $stemmer->stem($word);
# get list of stems for list of words
@stems = $stemmer->stem(@words);
DESCRIPTION
This module aims to provide a simple unified interface to any stemmer on
CPAN. It will provide a default available source module when a language
is requested but no source is requested.
Attributes
language
The following language codes are currently supported.
┌────────────┬────┐
│ Bulgarian │ bg │
│ Czech │ cs │
│ Danish │ da │
│ Dutch │ nl │
│ English │ en │
│ Esperanto │ eo │
│ Finnish │ fi │
│ French │ fr │
│ Galician │ gl │
│ German │ de │
│ Hungarian │ hu │
│ Ido │ io │
│ Italian │ it │
│ Latin │ la │
│ Norwegian │ no │
│ Persian │ fa │
│ Portuguese │ pt │
│ Romanian │ ro │
│ Russian │ ru │
│ Spanish │ es │
│ Swedish │ sv │
│ Turkish │ tr │
└────────────┴────┘
They are in the two-letter ISO 639-1 format and are case-insensitive
but are always returned in lowercase when requested.
# instantiate a stemmer object
$stemmer = Lingua::Stem::Any->new(language => $language);
# get current language
$language = $stemmer->language;
# change language
$stemmer->language($language);
The default language is "en" (English). The values "nb" (Norwegian
Bokmål) and "nn" (Norwegian Nynorsk) are aliases for "no"
(Norwegian). Country codes such as "CZ" for the Czech Republic are
not supported, as opposed to "cs" for the Czech language, nor are
full IETF language tags or Unicode locale identifiers such as
"pt-PT" or "pt-BR".
source
The following source modules are currently supported.
┌────────────────────────┬──────────────────────────────────────────────┐
│ Module │ Languages │
├────────────────────────┼──────────────────────────────────────────────┤
│ Lingua::Stem::Snowball │ da de en es fi fr hu it nl no pt ro ru sv tr │
│ Lingua::Stem::UniNE │ bg cs de fa │
│ Lingua::Stem │ da de en fr gl it no pt ru sv │
│ Lingua::Stem::Patch │ eo io │
└────────────────────────┴──────────────────────────────────────────────┘
A module name is used to specify the source. If no source is
specified, the first available source in the above list with support
for the current language is used.
# get current source
$source = $stemmer->source;
# change source
$stemmer->source('Lingua::Stem::UniNE');
cache
Boolean value specifying whether to cache the stem for each word.
This will increase performance when stemming the same word multiple
times at the expense of increased memory consumption. When enabled,
the stems are cached for the life of the object or until the
"clear_cache" method is called. The same cache is not shared among
different languages, sources, or different instances of the stemmer
object.
exceptions
Exceptions may be desired to bypass stemming for specific words and
use predefined stems. For example, the plural English word "mice"
will not stem to the singular word "mouse" unless it is specified in
the exception dictionary. Another example is that by default the
word "pants" will stem to "pant" even though stemming is normally
not desired in this example. The exception dictionary can be
provided as a hashref where the keys are language codes and the
values are hashrefs of exceptions.
# instantiate stemmer object with exceptions
$stemmer = Lingua::Stem::Any->new(
language => 'en',
exceptions => {
en => {
mice => 'mouse',
pants => 'pants',
}
}
);
# add/change exceptions
$stemmer->exceptions(
en => {
mice => 'mouse',
pants => 'pants',
}
);
# alternately...
$stemmer->exceptions->{en} = {
mice => 'mouse',
pants => 'pants',
};
casefold
Boolean value specifying whether to apply Unicode casefolding to
words before stemming them. This is enabled by default and is
performed before normalization when also enabled.
normalize
Boolean value specifying whether to apply Unicode NFC normalization
to words before stemming them. This is enabled by default and is
performed after casefolding when also enabled.
Methods
stem
Accepts a list of strings, stems each string, and returns a list of
stems. The list returned will always have the same number of
elements in the same order as the list provided. When no stemming
rules apply to a word, the original word is returned.
@stems = $stemmer->stem(@words);
# get the stem for a single word
$stem = $stemmer->stem($word);
The words should be provided as character strings and the stems are
returned as character strings. Byte strings in arbitrary character
encodings are not supported.
stem_in_place
Accepts an array reference, stems each element, and replaces them
with the resulting stems.
$stemmer->stem_in_place(\@words);
This method is provided for potential optimization when a large
array of words is to be stemmed. The return value is not defined.
languages
Returns a list of supported two-letter language codes using
lowercase letters.
# all languages
@languages = $stemmer->languages;
# languages supported by Lingua::Stem::Snowball
@languages = $stemmer->languages('Lingua::Stem::Snowball');
sources
Returns a list of supported source module names.
# all sources
@sources = $stemmer->sources;
# sources that support English
@sources = $stemmer->sources('en');
clear_cache
Clears the stem cache for all languages and sources of this object
instance when the "cache" attribute is enabled. Does not affect
whether caching is enabled.
SEE ALSO
Lingua::Stem::Snowball, Lingua::Stem::UniNE, Lingua::Stem,
Lingua::Stem::Patch
AUTHOR
Nick Patch <
[email protected]>
This project is brought to you by Shutterstock
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COPYRIGHT AND LICENSE
© 2013–2014 Shutterstock, Inc.
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
