phpman > perldoc > Lingua::Stem::En(3pm)

NAME
    Lingua::Stem::En - Porter's stemming algorithm for 'generic' English

SYNOPSIS
        use Lingua::Stem::En;
        my $stems   = Lingua::Stem::En::stem({ -words => $word_list_reference,
                                            -locale => 'en',
                                        -exceptions => $exceptions_hash,
                                         });

DESCRIPTION
    This routine applies the Porter Stemming Algorithm to its parameters, returning the stemmed
    words.

    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.

CHANGES
     1999.06.15 - Changed to '.pm' module, moved into Lingua::Stem namespace,
                  optionalized the export of the 'stem' routine
                  into the caller's namespace, added named parameters

     1999.06.24 - Switch core implementation of the Porter stemmer to
                  the one written by Jim Richardson <jimr AT maths.au>

     2000.08.25 - 2.11 Added stemming cache

     2000.09.14 - 2.12 Fixed *major* :( implementation error of Porter's algorithm
                  Error was entirely my fault - I completely forgot to include
                  rule sets 2,3, and 4 starting with Lingua::Stem 0.30.
                  -- Jerilyn Franz

     2003.09.28 - 2.13 Corrected documentation error pointed out by Simon Cozens.

     2005.11.20 - 2.14 Changed rule declarations to conform to Perl style convention
                  for 'private' subroutines. Changed Exporter invokation to more
                  portable 'require' vice 'use'.

     2006.02.14 - 2.15 Added ability to pass word list by 'handle' for in-place stemming.

     2009.07.27 - 2.16 Documentation Fix

     2020.06.20 - 2.30 Version renumber for module consistency.

METHODS
    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 @words         = ( 'wordy', 'another' );
          my $stemmed_words = Lingua::Stem::En::stem({ -words => \@words,
                                                      -locale => 'en',
                                                  -exceptions => \%exceptions,
                                  });

        If the first element of @words is a list reference, then the stemming is performed 'in
        place' on that list (modifying the passed list directly instead of copying it to a new
        array).

        This is only useful if you do not need to keep the original list. If you do need to keep the
        original list, use the normal semantic of having 'stem' return a new list instead - that is
        faster than making your own copy and using the 'in place' semantics since the primary
        difference between 'in place' and 'by value' stemming is the creation of a copy of the
        original list. If you don't need the original list, then the 'in place' stemming is about
        60% faster.

        Example of 'in place' stemming:

          my $words         = [ 'wordy', 'another' ];
          my $stemmed_words = Lingua::Stem::En::stem({ -words => [$words],
                                  -locale => 'en',
                              -exceptions => \%exceptions,
                              });

        The 'in place' mode returns a reference to the original list with the words stemmed.

    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.

    clear_stem_cache;
        Clears the cache of stemmed words

NOTES
    This code is almost entirely derived from the Porter 2.1 module written by Jim Richardson.

SEE ALSO
     Lingua::Stem

AUTHOR
      Jim Richardson, University of Sydney
      jimr AT maths.au or http://www.maths.usyd.edu.au:8000/jimr.html

      Integration in Lingua::Stem by
      Jerilyn Franz, FreeRun Technologies,
      <cpan AT jerilyn.info>

COPYRIGHT
    Jim Richardson, University of Sydney Jerilyn Franz, FreeRun Technologies

    This code is freely available under the same terms as Perl.

BUGS
TODO