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• SnowballStemmer.java

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weka.core.stemmers.SnowballStemmer Maven / Gradle / Ivy

/*
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see .
 */

/*
 * SnowballStemmer.java
 * Copyright (C) 2005-2012 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.core.stemmers;

import java.lang.reflect.Method;
import java.util.Enumeration;
import java.util.Vector;

import weka.core.ClassDiscovery;
import weka.core.Option;
import weka.core.OptionHandler;
import weka.core.RevisionUtils;
import weka.core.Utils;
import weka.gui.GenericObjectEditor;

/**
 *  A wrapper class for the Snowball stemmers. Only
 * available if the Snowball classes are in the classpath.

 * If the class discovery is not dynamic, i.e., the property 'UseDynamic' in the
 * props file 'weka/gui/GenericPropertiesCreator.props' is 'false', then the
 * property 'org.tartarus.snowball.SnowballProgram' in the
 * 'weka/gui/GenericObjectEditor.props' file has to be uncommented as well. If
 * necessary you have to discover and fill in the snowball stemmers manually.
 * You can use the 'weka.core.ClassDiscovery' for this:

 * java weka.core.ClassDiscovery org.tartarus.snowball.SnowballProgram
 * org.tartarus.snowball.ext

 * 

 * For more information visit these web sites:

 * http://weka.wikispaces.com/Stemmers

 * http://snowball.tartarus.org/

 * 

 * 
 * 
 *  Valid options are:
 * 

 * 
 * 
 * -S <name>
 *  The name of the snowball stemmer (default 'porter').
 *  available stemmers:
 *     danish, dutch, english, finnish, french, german, italian, 
 *     norwegian, porter, portuguese, russian, spanish, swedish
 * 
 * 
 * 
 * 
 * @author FracPete (fracpete at waikato dot ac dot nz)
 * @version $Revision: 10203 $
 */
public class SnowballStemmer implements Stemmer, OptionHandler {

  /** for serialization. */
  static final long serialVersionUID = -6111170431963015178L;

  /** the package name for snowball. */
  public final static String PACKAGE = "org.tartarus.snowball";

  /** the package name where the stemmers are located. */
  public final static String PACKAGE_EXT = PACKAGE + ".ext";

  /** the snowball program, all stemmers are derived from. */
  protected final static String SNOWBALL_PROGRAM = PACKAGE + ".SnowballProgram";

  /** whether the snowball stemmers are in the Classpath. */
  protected static boolean m_Present = false;

  /** contains the all the found stemmers (language names). */
  protected static Vector m_Stemmers;

  /** the current stemmer. */
  protected Object m_Stemmer;

  /** the stem method. */
  protected transient Method m_StemMethod;

  /** the setCurrent method. */
  protected transient Method m_SetCurrentMethod;

  /** the getCurrent method. */
  protected transient Method m_GetCurrentMethod;

  /** check for Snowball statically (needs only to be done once) */
  static {
    checkForSnowball();
  }

  /**
   * initializes the stemmer ("porter").
   */
  public SnowballStemmer() {
    this("porter");
    initStemmers();
  }

  /**
   * initializes the stemmer with the given stemmer.
   * 
   * @param name the name of the stemmer
   */
  public SnowballStemmer(String name) {
    super();

    setStemmer(name);
  }

  /**
   * checks whether Snowball is present in the classpath.
   */
  private static void checkForSnowball() {
    try {
      Class.forName(SNOWBALL_PROGRAM);
      m_Present = true;
    } catch (Exception e) {
      m_Present = false;
    }
  }

  /**
   * Returns a string describing the stemmer.
   * 
   * @return a description suitable for displaying in the explorer/experimenter
   *         gui
   */
  public String globalInfo() {
    return "A wrapper class for the Snowball stemmers. Only available if the "
      + "Snowball classes are in the classpath.\n"
      + "If the class discovery is not dynamic, i.e., the property 'UseDynamic' "
      + "in the props file 'weka/gui/GenericPropertiesCreator.props' is 'false', "
      + "then the property 'org.tartarus.snowball.SnowballProgram' in the "
      + "'weka/gui/GenericObjectEditor.props' file has to be uncommented "
      + "as well. If necessary you have to discover and fill in the snowball "
      + "stemmers manually. You can use the 'weka.core.ClassDiscovery' for this:\n"
      + "  java weka.core.ClassDiscovery org.tartarus.snowball.SnowballProgram org.tartarus.snowball.ext\n"
      + "\n" + "For more information visit these web sites:\n"
      + "  http://weka.wikispaces.com/Stemmers\n"
      + "  http://snowball.tartarus.org/\n";
  }

  /**
   * Returns an enumeration describing the available options.
   * 
   * @return an enumeration of all the available options.
   */
  @Override
  public Enumeration listOptions() {
    Vector result = new Vector();

    result.addElement(new Option(
      "\tThe name of the snowball stemmer (default 'porter').\n"
        + "\tavailable stemmers:\n" + getStemmerList(65, "\t   "), "S", 1,
      "-S "));

    return result.elements();
  }

  /**
   * Parses the options.
   * 

   * 
   *  Valid options are:
   * 

   * 
   * 
   * -S <name>
   *  The name of the snowball stemmer (default 'porter').
   *  available stemmers:
   *     danish, dutch, english, finnish, french, german, italian, 
   *     norwegian, porter, portuguese, russian, spanish, swedish
   * 
   * 
   * 
   * 
   * @param options the options to parse
   * @throws Exception if parsing fails
   */
  @Override
  public void setOptions(String[] options) throws Exception {
    String tmpStr;

    tmpStr = Utils.getOption('S', options);
    if (tmpStr.length() != 0) {
      setStemmer(tmpStr);
    } else {
      setStemmer("porter");
    }
  }

  /**
   * Gets the current settings of the classifier.
   * 
   * @return an array of strings suitable for passing to setOptions
   */
  @Override
  public String[] getOptions() {
    Vector result;

    result = new Vector();

    if (getStemmer() != null) {
      result.add("-S");
      result.add("" + getStemmer());
    }

    return result.toArray(new String[result.size()]);
  }

  /**
   * extracts the stemmer name form the classname.
   * 
   * @param classname the full classname of the stemmer
   * @return the name of the stemmer
   */
  private static String getStemmerName(String classname) {
    return classname.replaceAll(".*\\.", "").replaceAll("Stemmer$", "");
  }

  /**
   * returns the full classname of the stemmer.
   * 
   * @param name the name of the stemmer
   * @return the full classname of the stemmer
   * @see #PACKAGE_EXT
   */
  private static String getStemmerClassname(String name) {
    return PACKAGE_EXT + "." + name + "Stemmer";
  }

  /**
   * retrieves the language names of the availabel stemmers.
   */
  private static void initStemmers() {
    Vector classnames;
    int i;

    if (m_Stemmers != null) {
      return;
    }

    m_Stemmers = new Vector();

    if (!m_Present) {
      return;
    }

    classnames = GenericObjectEditor.getClassnames(SNOWBALL_PROGRAM);
    // try dynamic discovery if not in props file
    if (classnames.size() == 0) {
      classnames = ClassDiscovery.find(SNOWBALL_PROGRAM, PACKAGE_EXT);
      for (i = 0; i < classnames.size(); i++) {
        m_Stemmers.add(getStemmerName(classnames.get(i).toString()));
      }
    }
  }

  /**
   * returns whether Snowball is present or not, i.e. whether the classes are in
   * the classpath or not
   * 
   * @return whether Snowball is available
   */
  public static boolean isPresent() {
    return m_Present;
  }

  /**
   * returns an enumeration over all currently stored stemmer names.
   * 
   * @return all available stemmers
   */
  public static Enumeration listStemmers() {
    initStemmers();

    return m_Stemmers.elements();
  }

  /**
   * generates a comma list of the available stemmers.
   * 
   * @param lineLength the max line length, before a linefeed is inserted (0 is
   *          unlimited)
   * @param indention the indention of a line
   * @return the generated list
   */
  private static String getStemmerList(int lineLength, String indention) {
    String result;
    Enumeration enm;
    String name;
    String line;

    result = "";
    line = "";
    enm = listStemmers();
    while (enm.hasMoreElements()) {
      name = enm.nextElement().toString();
      if (line.length() > 0) {
        line += ", ";
      }
      if ((lineLength > 0) && (line.length() + name.length() > lineLength)) {
        result += indention + line + "\n";
        line = "";
      }
      line += name;
    }

    if (line.length() > 0) {
      result += indention + line + "\n";
    }

    return result;
  }

  /**
   * returns the name of the current stemmer, null if none is set.
   * 
   * @return the name of the stemmer
   */
  public String getStemmer() {
    initStemmers();

    if (m_Stemmer == null) {
      return null;
    } else {
      return getStemmerName(m_Stemmer.getClass().getName());
    }
  }

  /**
   * sets the stemmer with the given name, e.g., "porter".
   * 
   * @param name the name of the stemmer, e.g., "porter"
   */
  public void setStemmer(String name) {
    Class snowballClass;
    Class[] argClasses;

    initStemmers();

    if (m_Stemmers.contains(name)) {
      try {
        snowballClass = Class.forName(getStemmerClassname(name));
        m_Stemmer = snowballClass.newInstance();

        // methods
        argClasses = new Class[0];
        m_StemMethod = snowballClass.getMethod("stem", argClasses);

        argClasses = new Class[1];
        argClasses[0] = String.class;
        m_SetCurrentMethod = snowballClass.getMethod("setCurrent", argClasses);

        argClasses = new Class[0];
        m_GetCurrentMethod = snowballClass.getMethod("getCurrent", argClasses);
      } catch (Exception e) {
        System.out.println("Error initializing stemmer '" + name + "'!"
          + e.getMessage());
        m_Stemmer = null;
      }
    } else {
      System.err.println("Stemmer '" + name + "' unknown!");
      m_Stemmer = null;
    }
  }

  /**
   * Returns the tip text for this property.
   * 
   * @return tip text for this property suitable for displaying in the
   *         explorer/experimenter gui
   */
  public String stemmerTipText() {
    return "The Snowball stemmer to use, available: " + getStemmerList(0, "");
  }

  /**
   * Returns the word in its stemmed form.
   * 
   * @param word the unstemmed word
   * @return the stemmed word
   */
  @Override
  public String stem(String word) {
    String result;
    Object[] args;

    if (m_Stemmer == null) {
      result = new String(word);
    } else {
      // after de-serialization, the methods are null and need to be
      // re-initialized
      if (m_SetCurrentMethod == null) {
        setStemmer(getStemmer());
      }

      try {
        // set word
        args = new Object[1];
        args[0] = word;
        m_SetCurrentMethod.invoke(m_Stemmer, args);

        // stem word
        args = new Object[0];
        m_StemMethod.invoke(m_Stemmer, args);

        // get word
        args = new Object[0];
        result = (String) m_GetCurrentMethod.invoke(m_Stemmer, args);
      } catch (Exception e) {
        e.printStackTrace();
        result = word;
      }
    }

    return result;
  }

  /**
   * returns a string representation of the stemmer.
   * 
   * @return a string representation of the stemmer
   */
  @Override
  public String toString() {
    String result;

    result = getClass().getName();
    result += " " + Utils.joinOptions(getOptions());

    return result.trim();
  }

  /**
   * Returns the revision string.
   * 
   * @return the revision
   */
  @Override
  public String getRevision() {
    return RevisionUtils.extract("$Revision: 10203 $");
  }

  /**
   * Runs the stemmer with the given options.
   * 
   * @param args the options
   */
  public static void main(String[] args) {
    try {
      Stemming.useStemmer(new SnowballStemmer(), args);
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}