/*
* 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 <http://www.gnu.org/licenses/>.
*/
/*
* NaiveBayesMultinomialUpdateable.java
* Copyright (C) 2003-2012 University of Waikato, Hamilton, New Zealand
* Copyright (C) 2007 Jiang Su (incremental version)
*/
package weka.classifiers.bayes;
import weka.classifiers.UpdateableClassifier;
import weka.core.Instance;
import weka.core.Instances;
import weka.core.RevisionUtils;
import weka.core.Utils;
/**
<!-- globalinfo-start -->
* Class for building and using a multinomial Naive Bayes classifier. For more information see,<br/>
* <br/>
* Andrew Mccallum, Kamal Nigam: A Comparison of Event Models for Naive Bayes Text Classification. In: AAAI-98 Workshop on 'Learning for Text Categorization', 1998.<br/>
* <br/>
* The core equation for this classifier:<br/>
* <br/>
* P[Ci|D] = (P[D|Ci] x P[Ci]) / P[D] (Bayes rule)<br/>
* <br/>
* where Ci is class i and D is a document.<br/>
* <br/>
* Incremental version of the algorithm.
* <p/>
<!-- globalinfo-end -->
*
<!-- technical-bibtex-start -->
* BibTeX:
* <pre>
* @inproceedings{Mccallum1998,
* author = {Andrew Mccallum and Kamal Nigam},
* booktitle = {AAAI-98 Workshop on 'Learning for Text Categorization'},
* title = {A Comparison of Event Models for Naive Bayes Text Classification},
* year = {1998}
* }
* </pre>
* <p/>
<!-- technical-bibtex-end -->
*
<!-- options-start -->
* Valid options are: <p/>
*
* <pre> -D
* If set, classifier is run in debug mode and
* may output additional info to the console</pre>
*
<!-- options-end -->
*
* @author Andrew Golightly (acg4@cs.waikato.ac.nz)
* @author Bernhard Pfahringer (bernhard@cs.waikato.ac.nz)
* @author Jiang Su
* @version $Revision: 9412 $
*/
public class NaiveBayesMultinomialUpdateable
extends NaiveBayesMultinomial
implements UpdateableClassifier {
/** for serialization */
private static final long serialVersionUID = -7204398796974263186L;
/** the word count per class */
protected double[] m_wordsPerClass;
/**
* Returns a string describing this classifier
*
* @return a description of the classifier suitable for
* displaying in the explorer/experimenter gui
*/
public String globalInfo() {
return
super.globalInfo() + "\n\n"
+ "Incremental version of the algorithm.";
}
/**
* Generates the classifier.
*
* @param instances set of instances serving as training data
* @throws Exception if the classifier has not been generated successfully
*/
public void buildClassifier(Instances instances) throws Exception {
// can classifier handle the data?
getCapabilities().testWithFail(instances);
// remove instances with missing class
instances = new Instances(instances);
instances.deleteWithMissingClass();
m_headerInfo = new Instances(instances, 0);
m_numClasses = instances.numClasses();
m_numAttributes = instances.numAttributes();
m_probOfWordGivenClass = new double[m_numClasses][];
m_wordsPerClass = new double[m_numClasses];
m_probOfClass = new double[m_numClasses];
// initialising the matrix of word counts
// NOTE: Laplace estimator introduced in case a word that does not
// appear for a class in the training set does so for the test set
double laplace = 1;
for (int c = 0; c < m_numClasses; c++) {
m_probOfWordGivenClass[c] = new double[m_numAttributes];
m_probOfClass[c] = laplace;
m_wordsPerClass[c] = laplace * m_numAttributes;
for(int att = 0; att<m_numAttributes; att++) {
m_probOfWordGivenClass[c][att] = laplace;
}
}
for (int i = 0; i < instances.numInstances(); i++)
updateClassifier(instances.instance(i));
}
/**
* Updates the classifier with the given instance.
*
* @param instance the new training instance to include in the model
* @throws Exception if the instance could not be incorporated in
* the model.
*/
public void updateClassifier(Instance instance) throws Exception {
int classIndex = (int) instance.value(instance.classIndex());
m_probOfClass[classIndex] += instance.weight();
for (int a = 0; a < instance.numValues(); a++) {
if (instance.index(a) == instance.classIndex() ||
instance.isMissing(a))
continue;
double numOccurences = instance.valueSparse(a) * instance.weight();
/*if (numOccurences < 0)
throw new Exception(
"Numeric attribute values must all be greater or equal to zero."); */
m_wordsPerClass[classIndex] += numOccurences;
if (m_wordsPerClass[classIndex] < 0) {
throw new Exception("Can't have a negative number of words for class "
+ (classIndex + 1));
}
m_probOfWordGivenClass[classIndex][instance.index(a)] += numOccurences;
if (m_probOfWordGivenClass[classIndex][instance.index(a)] < 0) {
throw new Exception("Can't have a negative conditional sum for attribute "
+ instance.index(a));
}
}
}
/**
* Calculates the class membership probabilities for the given test
* instance.
*
* @param instance the instance to be classified
* @return predicted class probability distribution
* @throws Exception if there is a problem generating the prediction
*/
public double[] distributionForInstance(Instance instance) throws Exception {
double[] probOfClassGivenDoc = new double[m_numClasses];
// calculate the array of log(Pr[D|C])
double[] logDocGivenClass = new double[m_numClasses];
for (int c = 0; c < m_numClasses; c++) {
logDocGivenClass[c] += Math.log(m_probOfClass[c]);
int allWords = 0;
for (int i = 0; i < instance.numValues(); i++) {
if (instance.index(i) == instance.classIndex())
continue;
double frequencies = instance.valueSparse(i);
allWords += frequencies;
logDocGivenClass[c] += frequencies *
Math.log(m_probOfWordGivenClass[c][instance.index(i)]);
}
logDocGivenClass[c] -= allWords * Math.log(m_wordsPerClass[c]);
}
double max = logDocGivenClass[Utils.maxIndex(logDocGivenClass)];
for (int i = 0; i < m_numClasses; i++)
probOfClassGivenDoc[i] = Math.exp(logDocGivenClass[i] - max);
Utils.normalize(probOfClassGivenDoc);
return probOfClassGivenDoc;
}
/**
* Returns a string representation of the classifier.
*
* @return a string representation of the classifier
*/
public String toString() {
StringBuffer result = new StringBuffer();
result.append("The independent probability of a class\n");
result.append("--------------------------------------\n");
for (int c = 0; c < m_numClasses; c++)
result.append(m_headerInfo.classAttribute().value(c)).append("\t").
append(Double.toString(m_probOfClass[c])).append("\n");
result.append("\nThe probability of a word given the class\n");
result.append("-----------------------------------------\n\t");
for (int c = 0; c < m_numClasses; c++)
result.append(m_headerInfo.classAttribute().value(c)).append("\t");
result.append("\n");
for (int w = 0; w < m_numAttributes; w++) {
result.append(m_headerInfo.attribute(w).name()).append("\t");
for (int c = 0; c < m_numClasses; c++)
result.append(
Double.toString(Math.exp(m_probOfWordGivenClass[c][w]))).append("\t");
result.append("\n");
}
return result.toString();
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 9412 $");
}
/**
* Main method for testing this class.
*
* @param args the options
*/
public static void main(String[] args) {
runClassifier(new NaiveBayesMultinomialUpdateable(), args);
}
}