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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 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 .
 */

/*
 * SearchAlgorithm.java
 * Copyright (C) 2003-2012 University of Waikato, Hamilton, New Zealand
 * 
 */
package weka.classifiers.bayes.net.search;

import java.io.Serializable;
import java.util.Enumeration;
import java.util.Vector;

import weka.classifiers.bayes.BayesNet;
import weka.classifiers.bayes.net.BIFReader;
import weka.classifiers.bayes.net.ParentSet;
import weka.core.Instances;
import weka.core.Option;
import weka.core.OptionHandler;
import weka.core.RevisionHandler;
import weka.core.RevisionUtils;

/**
 * This is the base class for all search algorithms for learning Bayes networks.
 * It contains some common code, used by other network structure search
 * algorithms, and should not be used by itself.
 * 
 *  
 * 
 * @author Remco Bouckaert
 * @version $Revision: 10153 $
 */
public class SearchAlgorithm implements OptionHandler, Serializable,
  RevisionHandler {

  /** for serialization */
  static final long serialVersionUID = 6164792240778525312L;

  /**
   * Holds upper bound on number of parents
   */
  protected int m_nMaxNrOfParents = 1;

  /**
   * determines whether initial structure is an empty graph or a Naive Bayes
   * network
   */
  protected boolean m_bInitAsNaiveBayes = true;

  /**
   * Determines whether after structure is found a MarkovBlanketClassifier
   * correction should be applied If this is true, m_bInitAsNaiveBayes is
   * overridden and interpreted as false.
   */
  protected boolean m_bMarkovBlanketClassifier = false;

  /**
   * File name containing initial network structure. This can be used as
   * starting point for structure search It will be ignored if not speficied.
   * When specified, it overrides the InitAsNaivBayes flag.
   */
  protected String m_sInitalBIFFile;

  /** c'tor **/
  public SearchAlgorithm() {
  } // SearchAlgorithm

  /**
   * AddArcMakesSense checks whether adding the arc from iAttributeTail to
   * iAttributeHead does not already exists and does not introduce a cycle
   * 
   * @param bayesNet
   * @param instances
   * @param iAttributeHead index of the attribute that becomes head of the arrow
   * @param iAttributeTail index of the attribute that becomes tail of the arrow
   * @return true if adding arc is allowed, otherwise false
   */
  protected boolean addArcMakesSense(BayesNet bayesNet, Instances instances,
    int iAttributeHead, int iAttributeTail) {
    if (iAttributeHead == iAttributeTail) {
      return false;
    }

    // sanity check: arc should not be in parent set already
    if (isArc(bayesNet, iAttributeHead, iAttributeTail)) {
      return false;
    }

    // sanity check: arc should not introduce a cycle
    int nNodes = instances.numAttributes();
    boolean[] bDone = new boolean[nNodes];

    for (int iNode = 0; iNode < nNodes; iNode++) {
      bDone[iNode] = false;
    }

    // check for cycles
    bayesNet.getParentSet(iAttributeHead).addParent(iAttributeTail, instances);

    for (int iNode = 0; iNode < nNodes; iNode++) {

      // find a node for which all parents are 'done'
      boolean bFound = false;

      for (int iNode2 = 0; !bFound && iNode2 < nNodes; iNode2++) {
        if (!bDone[iNode2]) {
          boolean bHasNoParents = true;

          for (int iParent = 0; iParent < bayesNet.getParentSet(iNode2)
            .getNrOfParents(); iParent++) {
            if (!bDone[bayesNet.getParentSet(iNode2).getParent(iParent)]) {
              bHasNoParents = false;
            }
          }

          if (bHasNoParents) {
            bDone[iNode2] = true;
            bFound = true;
          }
        }
      }

      if (!bFound) {
        bayesNet.getParentSet(iAttributeHead).deleteLastParent(instances);

        return false;
      }
    }

    bayesNet.getParentSet(iAttributeHead).deleteLastParent(instances);

    return true;
  } // AddArcMakesCycle

  /**
   * reverseArcMakesSense checks whether the arc from iAttributeTail to
   * iAttributeHead exists and reversing does not introduce a cycle
   * 
   * @param bayesNet
   * @param instances
   * @param iAttributeHead index of the attribute that is head of the arrow
   * @param iAttributeTail index of the attribute that is tail of the arrow
   * @return true if the arc from iAttributeTail to iAttributeHead exists and
   *         reversing does not introduce a cycle
   */
  protected boolean reverseArcMakesSense(BayesNet bayesNet,
    Instances instances, int iAttributeHead, int iAttributeTail) {

    if (iAttributeHead == iAttributeTail) {
      return false;
    }

    // sanity check: arc should be in parent set already
    if (!isArc(bayesNet, iAttributeHead, iAttributeTail)) {
      return false;
    }

    // sanity check: arc should not introduce a cycle
    int nNodes = instances.numAttributes();
    boolean[] bDone = new boolean[nNodes];

    for (int iNode = 0; iNode < nNodes; iNode++) {
      bDone[iNode] = false;
    }

    // check for cycles
    bayesNet.getParentSet(iAttributeTail).addParent(iAttributeHead, instances);

    for (int iNode = 0; iNode < nNodes; iNode++) {

      // find a node for which all parents are 'done'
      boolean bFound = false;

      for (int iNode2 = 0; !bFound && iNode2 < nNodes; iNode2++) {
        if (!bDone[iNode2]) {
          ParentSet parentSet = bayesNet.getParentSet(iNode2);
          boolean bHasNoParents = true;
          for (int iParent = 0; iParent < parentSet.getNrOfParents(); iParent++) {
            if (!bDone[parentSet.getParent(iParent)]) {

              // this one has a parent which is not 'done' UNLESS it is the arc
              // to be reversed
              if (!(iNode2 == iAttributeHead && parentSet.getParent(iParent) == iAttributeTail)) {
                bHasNoParents = false;
              }
            }
          }

          if (bHasNoParents) {
            bDone[iNode2] = true;
            bFound = true;
          }
        }
      }

      if (!bFound) {
        bayesNet.getParentSet(iAttributeTail).deleteLastParent(instances);
        return false;
      }
    }

    bayesNet.getParentSet(iAttributeTail).deleteLastParent(instances);
    return true;
  } // ReverseArcMakesCycle

  /**
   * IsArc checks whether the arc from iAttributeTail to iAttributeHead already
   * exists
   * 
   * @param bayesNet
   * @param iAttributeHead index of the attribute that becomes head of the arrow
   * @param iAttributeTail index of the attribute that becomes tail of the arrow
   * @return true if the arc from iAttributeTail to iAttributeHead already
   *         exists
   */
  protected boolean isArc(BayesNet bayesNet, int iAttributeHead,
    int iAttributeTail) {
    for (int iParent = 0; iParent < bayesNet.getParentSet(iAttributeHead)
      .getNrOfParents(); iParent++) {
      if (bayesNet.getParentSet(iAttributeHead).getParent(iParent) == iAttributeTail) {
        return true;
      }
    }

    return false;
  } // IsArc

  /**
   * Returns an enumeration describing the available options.
   * 
   * @return an enumeration of all the available options.
   */
  @Override
  public Enumeration

   * 
   * @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 {
  } // setOptions

  /**
   * Gets the current settings of the Classifier.
   * 
   * @return an array of strings suitable for passing to setOptions
   */
  @Override
  public String[] getOptions() {
    return new String[0];
  } // getOptions

  /**
   * a string representation of the algorithm
   * 
   * @return a string representation
   */
  @Override
  public String toString() {
    return "SearchAlgorithm\n";
  } // toString

  /**
   * buildStructure determines the network structure/graph of the network. The
   * default behavior is creating a network where all nodes have the first node
   * as its parent (i.e., a BayesNet that behaves like a naive Bayes
   * classifier). This method can be overridden by derived classes to restrict
   * the class of network structures that are acceptable.
   * 
   * @param bayesNet the network
   * @param instances the data to use
   * @throws Exception if something goes wrong
   */
  public void buildStructure(BayesNet bayesNet, Instances instances)
    throws Exception {
    if (m_sInitalBIFFile != null && !m_sInitalBIFFile.equals("")) {
      BIFReader initialNet = new BIFReader().processFile(m_sInitalBIFFile);
      for (int iAttribute = 0; iAttribute < instances.numAttributes(); iAttribute++) {
        int iNode = initialNet.getNode(bayesNet.getNodeName(iAttribute));
        for (int iParent = 0; iParent < initialNet.getNrOfParents(iAttribute); iParent++) {
          String sParent = initialNet.getNodeName(initialNet.getParent(iNode,
            iParent));
          int nParent = 0;
          while (nParent < bayesNet.getNrOfNodes()
            && !bayesNet.getNodeName(nParent).equals(sParent)) {
            nParent++;
          }
          if (nParent < bayesNet.getNrOfNodes()) {
            bayesNet.getParentSet(iAttribute).addParent(nParent, instances);
          } else {
            System.err
              .println("Warning: Node "
                + sParent
                + " is ignored. It is found in initial network but not in data set.");
          }
        }
      }
    } else if (m_bInitAsNaiveBayes) {
      int iClass = instances.classIndex();
      // initialize parent sets to have arrow from classifier node to
      // each of the other nodes
      for (int iAttribute = 0; iAttribute < instances.numAttributes(); iAttribute++) {
        if (iAttribute != iClass) {
          bayesNet.getParentSet(iAttribute).addParent(iClass, instances);
        }
      }
    }
    search(bayesNet, instances);
    if (m_bMarkovBlanketClassifier) {
      doMarkovBlanketCorrection(bayesNet, instances);
    }
  } // buildStructure

  /**
   * 
   * @param bayesNet
   * @param instances
   */
  protected void search(BayesNet bayesNet, Instances instances)
    throws Exception {
    // placeholder with implementation in derived classes
  } // search

  /**
   * for each node in the network make sure it is in the Markov blanket of the
   * classifier node, and if not, add arrows so that it is. If the node is an
   * ancestor of the classifier node, add arrow pointing to the classifier node,
   * otherwise, add arrow pointing to attribute node.
   * 
   * @param bayesNet
   * @param instances
   */
  protected void doMarkovBlanketCorrection(BayesNet bayesNet,
    Instances instances) {
    // Add class node as parent if it is not in the Markov Boundary
    int iClass = instances.classIndex();
    ParentSet ancestors = new ParentSet();
    int nOldSize = 0;
    ancestors.addParent(iClass, instances);
    while (nOldSize != ancestors.getNrOfParents()) {
      nOldSize = ancestors.getNrOfParents();
      for (int iNode = 0; iNode < nOldSize; iNode++) {
        int iCurrent = ancestors.getParent(iNode);
        ParentSet p = bayesNet.getParentSet(iCurrent);
        for (int iParent = 0; iParent < p.getNrOfParents(); iParent++) {
          if (!ancestors.contains(p.getParent(iParent))) {
            ancestors.addParent(p.getParent(iParent), instances);
          }
        }
      }
    }
    for (int iAttribute = 0; iAttribute < instances.numAttributes(); iAttribute++) {
      boolean bIsInMarkovBoundary = (iAttribute == iClass)
        || bayesNet.getParentSet(iAttribute).contains(iClass)
        || bayesNet.getParentSet(iClass).contains(iAttribute);
      for (int iAttribute2 = 0; !bIsInMarkovBoundary
        && iAttribute2 < instances.numAttributes(); iAttribute2++) {
        bIsInMarkovBoundary = bayesNet.getParentSet(iAttribute2).contains(
          iAttribute)
          && bayesNet.getParentSet(iAttribute2).contains(iClass);
      }
      if (!bIsInMarkovBoundary) {
        if (ancestors.contains(iAttribute)) {
          if (bayesNet.getParentSet(iClass).getCardinalityOfParents() < 1024) {
            bayesNet.getParentSet(iClass).addParent(iAttribute, instances);
          } else {
            // too bad
          }
        } else {
          bayesNet.getParentSet(iAttribute).addParent(iClass, instances);
        }
      }
    }
  } // doMarkovBlanketCorrection

  /**
   * 
   * @param bMarkovBlanketClassifier
   */
  protected void setMarkovBlanketClassifier(boolean bMarkovBlanketClassifier) {
    m_bMarkovBlanketClassifier = bMarkovBlanketClassifier;
  }

  /**
   * 
   * @return
   */
  protected boolean getMarkovBlanketClassifier() {
    return m_bMarkovBlanketClassifier;
  }

  /**
   * @return a string to describe the MaxNrOfParentsoption.
   */
  public String maxNrOfParentsTipText() {
    return "Set the maximum number of parents a node in the Bayes net can have."
      + " When initialized as Naive Bayes, setting this parameter to 1 results in"
      + " a Naive Bayes classifier. When set to 2, a Tree Augmented Bayes Network (TAN)"
      + " is learned, and when set >2, a Bayes Net Augmented Bayes Network (BAN)"
      + " is learned. By setting it to a value much larger than the number of nodes"
      + " in the network (the default of 100000 pretty much guarantees this), no"
      + " restriction on the number of parents is enforced";
  } // maxNrOfParentsTipText

  /**
   * @return a string to describe the InitAsNaiveBayes option.
   */
  public String initAsNaiveBayesTipText() {
    return "When set to true (default), the initial network used for structure learning"
      + " is a Naive Bayes Network, that is, a network with an arrow from the classifier"
      + " node to each other node. When set to false, an empty network is used as initial"
      + " network structure";
  } // initAsNaiveBayesTipText

  /**
   * @return a string to describe the MarkovBlanketClassifier option.
   */
  protected String markovBlanketClassifierTipText() {
    return "When set to true (default is false), after a network structure is learned"
      + " a Markov Blanket correction is applied to the network structure. This ensures"
      + " that all nodes in the network are part of the Markov blanket of the classifier"
      + " node.";
  } // markovBlanketClassifierTipText

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




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