source: src/main/java/weka/classifiers/trees/j48/NBTreeNoSplit.java @ 28

/*
 *    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.
 */

/*
 *    NBTreeNoSplit.java
 *    Copyright (C) 2004 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.classifiers.trees.j48;

import weka.classifiers.Classifier;
import weka.classifiers.AbstractClassifier;
import weka.classifiers.Evaluation;
import weka.classifiers.bayes.NaiveBayesUpdateable;
import weka.core.Instance;
import weka.core.Instances;
import weka.core.RevisionUtils;
import weka.filters.Filter;
import weka.filters.supervised.attribute.Discretize;

import java.util.Random;

/**
 * Class implementing a "no-split"-split (leaf node) for naive bayes
 * trees.
 *
 * @author Mark Hall (mhall@cs.waikato.ac.nz)
 * @version $Revision: 5928 $
 */
public final class NBTreeNoSplit
  extends ClassifierSplitModel {

  /** for serialization */
  private static final long serialVersionUID = 7824804381545259618L;

  /** the naive bayes classifier */
  private NaiveBayesUpdateable m_nb;

  /** the discretizer used */
  private Discretize m_disc;

  /** errors on the training data at this node */
  private double m_errors;

  public NBTreeNoSplit() {
    m_numSubsets = 1;
  }

  /**
   * Build the no-split node
   *
   * @param instances an <code>Instances</code> value
   * @exception Exception if an error occurs
   */
  public final void buildClassifier(Instances instances) throws Exception {
    m_nb = new NaiveBayesUpdateable();
    m_disc = new Discretize();
    m_disc.setInputFormat(instances);
    Instances temp = Filter.useFilter(instances, m_disc);
    m_nb.buildClassifier(temp);
    if (temp.numInstances() >= 5) {
      m_errors = crossValidate(m_nb, temp, new Random(1));
    }
    m_numSubsets = 1;
  }

  /**
   * Return the errors made by the naive bayes model at this node
   *
   * @return the number of errors made
   */
  public double getErrors() {
    return m_errors;
  }

  /**
   * Return the discretizer used at this node
   *
   * @return a <code>Discretize</code> value
   */
  public Discretize getDiscretizer() {
    return m_disc;
  }

  /**
   * Get the naive bayes model at this node
   *
   * @return a <code>NaiveBayesUpdateable</code> value
   */
  public NaiveBayesUpdateable getNaiveBayesModel() {
    return m_nb;
  }

  /**
   * Always returns 0 because only there is only one subset.
   */
  public final int whichSubset(Instance instance){
    
    return 0;
  }

  /**
   * Always returns null because there is only one subset.
   */
  public final double [] weights(Instance instance){

    return null;
  }
  
  /**
   * Does nothing because no condition has to be satisfied.
   */
  public final String leftSide(Instances instances){

    return "";
  }
  
  /**
   * Does nothing because no condition has to be satisfied.
   */
  public final String rightSide(int index, Instances instances){

    return "";
  }

  /**
   * Returns a string containing java source code equivalent to the test
   * made at this node. The instance being tested is called "i".
   *
   * @param index index of the nominal value tested
   * @param data the data containing instance structure info
   * @return a value of type 'String'
   */
  public final String sourceExpression(int index, Instances data) {

    return "true";  // or should this be false??
  }

  /**
   * Return the probability for a class value
   *
   * @param classIndex the index of the class value
   * @param instance the instance to generate a probability for
   * @param theSubset the subset to consider
   * @return a probability
   * @exception Exception if an error occurs
   */
  public double classProb(int classIndex, Instance instance, int theSubset) 
    throws Exception {
    m_disc.input(instance);
    Instance temp = m_disc.output();
    return m_nb.distributionForInstance(temp)[classIndex];
  }

  /**
   * Return a textual description of the node
   *
   * @return a <code>String</code> value
   */
  public String toString() {
    return m_nb.toString();
  }

  /**
   * Utility method for fast 5-fold cross validation of a naive bayes
   * model
   *
   * @param fullModel a <code>NaiveBayesUpdateable</code> value
   * @param trainingSet an <code>Instances</code> value
   * @param r a <code>Random</code> value
   * @return a <code>double</code> value
   * @exception Exception if an error occurs
   */
  public static double crossValidate(NaiveBayesUpdateable fullModel,
                               Instances trainingSet,
                               Random r) throws Exception {
    // make some copies for fast evaluation of 5-fold xval
    Classifier [] copies = AbstractClassifier.makeCopies(fullModel, 5);
    Evaluation eval = new Evaluation(trainingSet);
    // make some splits
    for (int j = 0; j < 5; j++) {
      Instances test = trainingSet.testCV(5, j);
      // unlearn these test instances
      for (int k = 0; k < test.numInstances(); k++) {
        test.instance(k).setWeight(-test.instance(k).weight());
        ((NaiveBayesUpdateable)copies[j]).updateClassifier(test.instance(k));
        // reset the weight back to its original value
        test.instance(k).setWeight(-test.instance(k).weight());
      }
      eval.evaluateModel(copies[j], test);
    }
    return eval.incorrect();
  }
  
  /**
   * Returns the revision string.
   * 
   * @return            the revision
   */
  public String getRevision() {
    return RevisionUtils.extract("$Revision: 5928 $");
  }
}