Class: Ferret::Analysis::StemFilter

Inherits:

Object

Object
Ferret::Analysis::StemFilter

show all

Defined in:: ext/r_analysis.c

Overview

Summary

A StemFilter takes a term and transforms the term as per the SnowBall stemming algorithm. Note: the input to the stemming filter must already be in lower case, so you will need to use LowerCaseFilter or lowercasing Tokenizer further down the Tokenizer chain in order for this to work properly!

Available algorithms and encodings

Algorithm       Algorithm Pseudonyms       Encoding
----------------------------------------------------------------
 "danish",     | "da", "dan"              | "ISO_8859_1", "UTF_8"
 "dutch",      | "dut", "nld"             | "ISO_8859_1", "UTF_8"
 "english",    | "en", "eng"              | "ISO_8859_1", "UTF_8"
 "finnish",    | "fi", "fin"              | "ISO_8859_1", "UTF_8"
 "french",     | "fr", "fra", "fre"       | "ISO_8859_1", "UTF_8"
 "german",     | "de", "deu", "ge", "ger" | "ISO_8859_1", "UTF_8"
 "hungarian",  | "hu", "hun"              | "ISO_8859_1", "UTF_8"
 "italian",    | "it", "ita"              | "ISO_8859_1", "UTF_8"
 "norwegian",  | "nl", "no"               | "ISO_8859_1", "UTF_8"
 "porter",     |                          | "ISO_8859_1", "UTF_8"
 "portuguese", | "por", "pt"              | "ISO_8859_1", "UTF_8"
 "romanian",   | "ro", "ron", "rum"       | "ISO_8859_2", "UTF_8"
 "russian",    | "ru", "rus"              | "KOI8_R",     "UTF_8"
 "spanish",    | "es", "esl"              | "ISO_8859_1", "UTF_8"
 "swedish",    | "sv", "swe"              | "ISO_8859_1", "UTF_8"
 "turkish",    | "tr", "tur"              |               "UTF_8"

New Stemmers

The following stemmers have recently benn added. Please try them out;

* Hungarian
* Romanian
* Turkish

Example

To use this filter with other analyzers, you’ll want to write an Analyzer class that sets up the TokenStream chain as you want it. To use this with a lowercasing Tokenizer, for example, you’d write an analyzer like this:

def MyAnalyzer < Analyzer
  def token_stream(field, str)
    return StemFilter.new(LowerCaseFilter.new(StandardTokenizer.new(str)))
  end
end

"debate debates debated debating debater"
  => ["debat", "debat", "debat", "debat", "debat"]

Attributes

token_stream: TokenStream to be filtered
algorithm: The algorithm (or language) to use (default: “english”)
encoding: The encoding of the data (default: “UTF-8”)