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The Waikato Environment for Knowledge Analysis (WEKA), a machine learning workbench. This version represents the developer version, the "bleeding edge" of development, you could say. New functionality gets added to this version.
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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 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 .
 */

/*
 *    PruneableDecList.java
 *    Copyright (C) 1999-2012 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.classifiers.rules.part;

import weka.classifiers.trees.j48.Distribution;
import weka.classifiers.trees.j48.ModelSelection;
import weka.classifiers.trees.j48.NoSplit;
import weka.core.Instances;
import weka.core.RevisionUtils;
import weka.core.Utils;

/**
 * Class for handling a partial tree structure that can be pruned using a
 * pruning set.
 * 
 * @author Eibe Frank ([email protected])
 * @version $Revision: 10153 $
 */
public class PruneableDecList extends ClassifierDecList {

  /** for serialization */
  private static final long serialVersionUID = -7228103346297172921L;

  /**
   * Constructor for pruneable partial tree structure.
   * 
   * @param toSelectLocModel selection method for local splitting model
   * @param minNum minimum number of objects in leaf
   */
  public PruneableDecList(ModelSelection toSelectLocModel, int minNum) {

    super(toSelectLocModel, minNum);
  }

  /**
   * Method for building a pruned partial tree.
   * 
   * @throws Exception if tree can't be built successfully
   */
  public void buildRule(Instances train, Instances test) throws Exception {

    buildDecList(train, test, false);

    cleanup(new Instances(train, 0));
  }

  /**
   * Builds the partial tree with hold out set
   * 
   * @throws Exception if something goes wrong
   */
  public void buildDecList(Instances train, Instances test, boolean leaf)
    throws Exception {

    Instances[] localTrain, localTest;
    int ind;
    int i, j;
    double sumOfWeights;
    NoSplit noSplit;

    m_train = null;
    m_isLeaf = false;
    m_isEmpty = false;
    m_sons = null;
    indeX = 0;
    sumOfWeights = train.sumOfWeights();
    noSplit = new NoSplit(new Distribution(train));
    if (leaf) {
      m_localModel = noSplit;
    } else {
      m_localModel = m_toSelectModel.selectModel(train, test);
    }
    m_test = new Distribution(test, m_localModel);
    if (m_localModel.numSubsets() > 1) {
      localTrain = m_localModel.split(train);
      localTest = m_localModel.split(test);
      train = null;
      test = null;
      m_sons = new ClassifierDecList[m_localModel.numSubsets()];
      i = 0;
      do {
        i++;
        ind = chooseIndex();
        if (ind == -1) {
          for (j = 0; j < m_sons.length; j++) {
            if (m_sons[j] == null) {
              m_sons[j] = getNewDecList(localTrain[j], localTest[j], true);
            }
          }
          if (i < 2) {
            m_localModel = noSplit;
            m_isLeaf = true;
            m_sons = null;
            if (Utils.eq(sumOfWeights, 0)) {
              m_isEmpty = true;
            }
            return;
          }
          ind = 0;
          break;
        } else {
          m_sons[ind] = getNewDecList(localTrain[ind], localTest[ind], false);
        }
      } while ((i < m_sons.length) && (m_sons[ind].m_isLeaf));

      // Check if all successors are leaves
      for (j = 0; j < m_sons.length; j++) {
        if ((m_sons[j] == null) || (!m_sons[j].m_isLeaf)) {
          break;
        }
      }
      if (j == m_sons.length) {
        pruneEnd();
        if (!m_isLeaf) {
          indeX = chooseLastIndex();
        }
      } else {
        indeX = chooseLastIndex();
      }
    } else {
      m_isLeaf = true;
      if (Utils.eq(sumOfWeights, 0)) {
        m_isEmpty = true;
      }
    }
  }

  /**
   * Returns a newly created tree.
   * 
   * @param train train data
   * @param test test data
   * @param leaf
   * @throws Exception if something goes wrong
   */
  protected ClassifierDecList getNewDecList(Instances train, Instances test,
    boolean leaf) throws Exception {

    PruneableDecList newDecList = new PruneableDecList(m_toSelectModel,
      m_minNumObj);

    newDecList.buildDecList(train, test, leaf);

    return newDecList;
  }

  /**
   * Prunes the end of the rule.
   */
  protected void pruneEnd() throws Exception {

    double errorsLeaf, errorsTree;

    errorsTree = errorsForTree();
    errorsLeaf = errorsForLeaf();
    if (Utils.smOrEq(errorsLeaf, errorsTree)) {
      m_isLeaf = true;
      m_sons = null;
      m_localModel = new NoSplit(localModel().distribution());
    }
  }

  /**
   * Computes error estimate for tree.
   */
  private double errorsForTree() throws Exception {

    if (m_isLeaf) {
      return errorsForLeaf();
    } else {
      double error = 0;
      for (int i = 0; i < m_sons.length; i++) {
        if (Utils.eq(son(i).localModel().distribution().total(), 0)) {
          error += m_test.perBag(i)
            - m_test.perClassPerBag(i, localModel().distribution().maxClass());
        } else {
          error += ((PruneableDecList) son(i)).errorsForTree();
        }
      }

      return error;
    }
  }

  /**
   * Computes estimated errors for leaf.
   */
  private double errorsForLeaf() throws Exception {

    return m_test.total()
      - m_test.perClass(localModel().distribution().maxClass());
  }

  /**
   * Returns the revision string.
   * 
   * @return the revision
   */
  @Override
  public String getRevision() {
    return RevisionUtils.extract("$Revision: 10153 $");
  }
}