---
name: "Lingua::Stem::En"
section: "3pm"
platform: "linux"
package: "liblingua-stem-perl"
version: "2.31-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Lingua::Stem::En"
---

# Lingua::Stem::En(3pm)

Porter's stemming algorithm for 'generic' English

## 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@maths.usyd.edu.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.
 2020.09.26 - 2.31 Fix for Latin1/UTF8 issue in documentation
```

## 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@maths.usyd.edu.au or http://www.maths.usyd.edu.au:8000/jimr.html
  Integration in Lingua::Stem by
  Jerilyn Franz, FreeRun Technologies,
  <cpan@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