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The Waikato Environment for Knowledge Analysis (WEKA), a machine learning workbench. This is the stable version. Apart from bugfixes, this version does not receive any other updates.
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/*
 *    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 2 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, write to the Free Software
 *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * NGramTokenizer.java
 * Copyright (C) 2007 University of Waikato
 */

package weka.core.tokenizers;

import java.util.Enumeration;
import java.util.LinkedList;
import java.util.Vector;

import weka.core.Option;
import weka.core.RevisionUtils;
import weka.core.Utils;

/**
 *  Splits a string into an n-gram with min and max
 * grams.
 * 
 * 
 * 
 *  Valid options are:
 * 

 * 
 * 
 * -delimiters <value>
 *  The delimiters to use
 *  (default ' \r\n\t.,;:'"()?!').
 * 
 * 
 *  * -max <int>
 *  The max size of the Ngram (default = 3).
 * 
 * 
 *  * -min <int>
 *  The min size of the Ngram (default = 1).
 * 
 * 
 * 
 * 
 * @author Sebastian Germesin ([email protected])
 * @author FracPete (fracpete at waikato dot ac dot nz)
 * @version $Revision: 1.4 $
 */
public class NGramTokenizer
  extends CharacterDelimitedTokenizer {

  /** for serialization */
  private static final long serialVersionUID = -2181896254171647219L;

  /** the maximum number of N */
  protected int m_NMax = 3;

  /** the minimum number of N */
  protected int m_NMin = 1;

  /** the current length of the N-grams */
  protected int m_N;

  /** the number of strings available */
  protected int m_MaxPosition;

  /** the current position for returning elements */
  protected int m_CurrentPosition;

  /** all the available grams */
  protected String[] m_SplitString;

  /**
   * Returns a string describing the stemmer
   * 
   * @return a description suitable for displaying in the explorer/experimenter
   *         gui
   */
  @Override
  public String globalInfo() {
    return "Splits a string into an n-gram with min and max grams.";
  }

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

    result = new Vector();

    enm = super.listOptions();
    while (enm.hasMoreElements()) {
      result.addElement(enm.nextElement());
    }

    result.addElement(new Option(
      "\tThe max size of the Ngram (default = 3).",
      "max", 1, "-max "));

    result.addElement(new Option(
      "\tThe min size of the Ngram (default = 1).",
      "min", 1, "-min "));

    return result.elements();
  }

  /**
   * Gets the current option settings for the OptionHandler.
   * 
   * @return the list of current option settings as an array of strings
   */
  @Override
  public String[] getOptions() {
    Vector result;
    String[] options;
    int i;

    result = new Vector();

    options = super.getOptions();
    for (i = 0; i < options.length; i++) {
      result.add(options[i]);
    }

    result.add("-max");
    result.add("" + getNGramMaxSize());

    result.add("-min");
    result.add("" + getNGramMinSize());

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

  /**
   * Parses a given list of options.
   * 
   * 
   *  Valid options are:
   * 

   * 
   * 
   * -delimiters <value>
   *  The delimiters to use
   *  (default ' \r\n\t.,;:'"()?!').
   * 
   * 
   *    * -max <int>
   *  The max size of the Ngram (default = 3).
   * 
   * 
   *    * -min <int>
   *  The min size of the Ngram (default = 1).
   * 
   * 
   * 
   * 
   * @param options the list of options as an array of strings
   * @throws Exception if an option is not supported
   */
  @Override
  public void setOptions(String[] options) throws Exception {
    String value;

    super.setOptions(options);

    value = Utils.getOption("max", options);
    if (value.length() != 0) {
      setNGramMaxSize(Integer.parseInt(value));
    } else {
      setNGramMaxSize(3);
    }

    value = Utils.getOption("min", options);
    if (value.length() != 0) {
      setNGramMinSize(Integer.parseInt(value));
    } else {
      setNGramMinSize(1);
    }
  }

  /**
   * Gets the max N of the NGram.
   * 
   * @return the size (N) of the NGram.
   */
  public int getNGramMaxSize() {
    return m_NMax;
  }

  /**
   * Sets the max size of the Ngram.
   * 
   * @param value the size of the NGram.
   */
  public void setNGramMaxSize(int value) {
    if (value < 1) {
      m_NMax = 1;
    } else {
      m_NMax = value;
    }
  }

  /**
   * Returns the tip text for this property.
   * 
   * @return tip text for this property suitable for displaying in the
   *         explorer/experimenter gui
   */
  public String NGramMaxSizeTipText() {
    return "The max N of the NGram.";
  }

  /**
   * Sets the min size of the Ngram.
   * 
   * @param value the size of the NGram.
   */
  public void setNGramMinSize(int value) {
    if (value < 1) {
      m_NMin = 1;
    } else {
      m_NMin = value;
    }
  }

  /**
   * Gets the min N of the NGram.
   * 
   * @return the size (N) of the NGram.
   */
  public int getNGramMinSize() {
    return m_NMin;
  }

  /**
   * Returns the tip text for this property.
   * 
   * @return tip text for this property suitable for displaying in the
   *         explorer/experimenter gui
   */
  public String NGramMinSizeTipText() {
    return "The min N of the NGram.";
  }

  /**
   * returns true if there's more elements available
   * 
   * @return true if there are more elements available
   */
  @Override
  public boolean hasMoreElements() {
    // return (m_CurrentPosition < m_MaxPosition &&
    // m_N - 1 + m_CurrentPosition < m_MaxPosition &&
    // m_N >= m_NMin);
    return (m_N >= m_NMin);
  }

  /**
   * Returns N-grams and also (N-1)-grams and .... and 1-grams.
   * 
   * @return the next element
   */
  @Override
  public Object nextElement() {
    String retValue = "";

    // for (int i = 0; i < m_N && i + m_CurrentPosition < m_MaxPosition; i++)
    // retValue += " " + m_SplitString[m_CurrentPosition + i];
    //
    for (int i = 0; i < m_N; i++) {
      retValue += " " + m_SplitString[m_CurrentPosition + i];
    }

    m_CurrentPosition++;

    if (m_CurrentPosition + m_N - 1 == m_MaxPosition) {
      m_CurrentPosition = 0;
      m_N--;
    }

    return retValue.trim();
  }

  /**
   * filters out empty strings in m_SplitString and replaces m_SplitString with
   * the cleaned version.
   * 
   * @see #m_SplitString
   */
  protected void filterOutEmptyStrings() {
    String[] newSplit;
    LinkedList clean = new LinkedList();

    for (int i = 0; i < m_SplitString.length; i++) {
      if (!m_SplitString[i].equals("")) {
        clean.add(m_SplitString[i]);
      }
    }

    newSplit = new String[clean.size()];
    for (int i = 0; i < clean.size(); i++) {
      newSplit[i] = clean.get(i);
    }

    m_SplitString = newSplit;
  }

  /**
   * Sets the string to tokenize. Tokenization happens immediately.
   * 
   * @param s the string to tokenize
   */
  @Override
  public void tokenize(String s) {
    m_N = m_NMax;
    m_SplitString = s.split("[" + getDelimiters() + "]");

    filterOutEmptyStrings();

    m_CurrentPosition = 0;
    m_MaxPosition = m_SplitString.length;

    if (m_SplitString.length < m_NMax) {
      m_N = m_SplitString.length;
    }
  }

  /**
   * Returns the revision string.
   * 
   * @return the revision
   */
  @Override
  public String getRevision() {
    return RevisionUtils.extract("$Revision: 1.4 $");
  }

  /**
   * Runs the tokenizer with the given options and strings to tokenize. The
   * tokens are printed to stdout.
   * 
   * @param args the commandline options and strings to tokenize
   */
  public static void main(String[] args) {
    runTokenizer(new NGramTokenizer(), args);
  }
}