/*
* 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.
*/
/*
* ComplementNaiveBayes.java
* Copyright (C) 2003 University of Waikato, Hamilton, New Zealand
*/
package weka.classifiers.bayes;
import weka.classifiers.Classifier;
import weka.core.Capabilities;
import weka.core.FastVector;
import weka.core.Instance;
import weka.core.Instances;
import weka.core.Option;
import weka.core.OptionHandler;
import weka.core.RevisionUtils;
import weka.core.TechnicalInformation;
import weka.core.TechnicalInformationHandler;
import weka.core.Utils;
import weka.core.WeightedInstancesHandler;
import weka.core.Capabilities.Capability;
import weka.core.TechnicalInformation.Field;
import weka.core.TechnicalInformation.Type;
/**
<!-- globalinfo-start -->
* Class for building and using a Complement class Naive Bayes classifier.<br/>
* <br/>
* For more information see, <br/>
* <br/>
* Jason D. Rennie, Lawrence Shih, Jaime Teevan, David R. Karger: Tackling the Poor Assumptions of Naive Bayes Text Classifiers. In: ICML, 616-623, 2003.<br/>
* <br/>
* P.S.: TF, IDF and length normalization transforms, as described in the paper, can be performed through weka.filters.unsupervised.StringToWordVector.
* <p/>
<!-- globalinfo-end -->
*
<!-- technical-bibtex-start -->
* BibTeX:
* <pre>
* @inproceedings{Rennie2003,
* author = {Jason D. Rennie and Lawrence Shih and Jaime Teevan and David R. Karger},
* booktitle = {ICML},
* pages = {616-623},
* publisher = {AAAI Press},
* title = {Tackling the Poor Assumptions of Naive Bayes Text Classifiers},
* year = {2003}
* }
* </pre>
* <p/>
<!-- technical-bibtex-end -->
*
<!-- options-start -->
* Valid options are: <p/>
*
* <pre> -N
* Normalize the word weights for each class
* </pre>
*
* <pre> -S
* Smoothing value to avoid zero WordGivenClass probabilities (default=1.0).
* </pre>
*
<!-- options-end -->
*
* @author Ashraf M. Kibriya (amk14@cs.waikato.ac.nz)
* @version $Revision: 1.9 $
*/
public class ComplementNaiveBayes extends Classifier
implements OptionHandler, WeightedInstancesHandler, TechnicalInformationHandler {
/** for serialization */
static final long serialVersionUID = 7246302925903086397L;
/**
Weight of words for each class. The weight is actually the
log of the probability of a word (w) given a class (c)
(i.e. log(Pr[w|c])). The format of the matrix is:
wordWeights[class][wordAttribute]
*/
private double[][] wordWeights;
/** Holds the smoothing value to avoid word probabilities of zero.<br>
P.S.: According to the paper this is the Alpha i parameter
*/
private double smoothingParameter = 1.0;
/** True if the words weights are to be normalized */
private boolean m_normalizeWordWeights = false;
/** Holds the number of Class values present in the set of specified
instances */
private int numClasses;
/** The instances header that'll be used in toString */
private Instances header;
/**
* Returns an enumeration describing the available options.
*
* @return an enumeration of all the available options.
*/
public java.util.Enumeration listOptions() {
FastVector newVector = new FastVector(2);
newVector.addElement(
new Option("\tNormalize the word weights for each class\n",
"N", 0,"-N"));
newVector.addElement(
new Option("\tSmoothing value to avoid zero WordGivenClass"+
" probabilities (default=1.0).\n",
"S", 1,"-S"));
return newVector.elements();
}
/**
* Gets the current settings of the classifier.
*
* @return an array of strings suitable for passing to setOptions
*/
public String[] getOptions() {
String options[] = new String[4];
int current=0;
if(getNormalizeWordWeights())
options[current++] = "-N";
options[current++] = "-S";
options[current++] = Double.toString(smoothingParameter);
while (current < options.length) {
options[current++] = "";
}
return options;
}
/**
* Parses a given list of options. <p/>
*
<!-- options-start -->
* Valid options are: <p/>
*
* <pre> -N
* Normalize the word weights for each class
* </pre>
*
* <pre> -S
* Smoothing value to avoid zero WordGivenClass probabilities (default=1.0).
* </pre>
*
<!-- options-end -->
*
* @param options the list of options as an array of strings
* @throws Exception if an option is not supported
*/
public void setOptions(String[] options) throws Exception {
setNormalizeWordWeights(Utils.getFlag('N', options));
String val = Utils.getOption('S', options);
if(val.length()!=0)
setSmoothingParameter(Double.parseDouble(val));
else
setSmoothingParameter(1.0);
}
/**
* Returns true if the word weights for each class are to be normalized
*
* @return true if the word weights are normalized
*/
public boolean getNormalizeWordWeights() {
return m_normalizeWordWeights;
}
/**
* Sets whether if the word weights for each class should be normalized
*
* @param doNormalize whether the word weights are to be normalized
*/
public void setNormalizeWordWeights(boolean doNormalize) {
m_normalizeWordWeights = doNormalize;
}
/**
* Returns the tip text for this property
* @return tip text for this property suitable for
* displaying in the explorer/experimenter gui
*/
public String normalizeWordWeightsTipText() {
return "Normalizes the word weights for each class.";
}
/**
* Gets the smoothing value to be used to avoid zero WordGivenClass
* probabilities.
*
* @return the smoothing value
*/
public double getSmoothingParameter() {
return smoothingParameter;
}
/**
* Sets the smoothing value used to avoid zero WordGivenClass probabilities
*
* @param val the new smooting value
*/
public void setSmoothingParameter(double val) {
smoothingParameter = val;
}
/**
* Returns the tip text for this property
* @return tip text for this property suitable for
* displaying in the explorer/experimenter gui
*/
public String smoothingParameterTipText() {
return "Sets the smoothing parameter to avoid zero WordGivenClass "+
"probabilities (default=1.0).";
}
/**
* Returns a string describing this classifier
* @return a description of the classifier suitable for
* displaying in the explorer/experimenter gui
*/
public String globalInfo() {
return "Class for building and using a Complement class Naive Bayes "+
"classifier.\n\nFor more information see, \n\n"+
getTechnicalInformation().toString() + "\n\n" +
"P.S.: TF, IDF and length normalization transforms, as "+
"described in the paper, can be performed through "+
"weka.filters.unsupervised.StringToWordVector.";
}
/**
* Returns an instance of a TechnicalInformation object, containing
* detailed information about the technical background of this class,
* e.g., paper reference or book this class is based on.
*
* @return the technical information about this class
*/
public TechnicalInformation getTechnicalInformation() {
TechnicalInformation result;
result = new TechnicalInformation(Type.INPROCEEDINGS);
result.setValue(Field.AUTHOR, "Jason D. Rennie and Lawrence Shih and Jaime Teevan and David R. Karger");
result.setValue(Field.TITLE, "Tackling the Poor Assumptions of Naive Bayes Text Classifiers");
result.setValue(Field.BOOKTITLE, "ICML");
result.setValue(Field.YEAR, "2003");
result.setValue(Field.PAGES, "616-623");
result.setValue(Field.PUBLISHER, "AAAI Press");
return result;
}
/**
* Returns default capabilities of the classifier.
*
* @return the capabilities of this classifier
*/
public Capabilities getCapabilities() {
Capabilities result = super.getCapabilities();
// attributes
result.enable(Capability.NUMERIC_ATTRIBUTES);
result.enable(Capability.MISSING_VALUES);
// class
result.enable(Capability.NOMINAL_CLASS);
result.enable(Capability.MISSING_CLASS_VALUES);
return result;
}
/**
* Generates the classifier.
*
* @param instances set of instances serving as training data
* @throws Exception if the classifier has not been built 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();
numClasses = instances.numClasses();
int numAttributes = instances.numAttributes();
header = new Instances(instances, 0);
double [][] ocrnceOfWordInClass = new double[numClasses][numAttributes];
wordWeights = new double[numClasses][numAttributes];
//double [] docsPerClass = new double[numClasses];
double[] wordsPerClass = new double[numClasses];
double totalWordOccurrences = 0;
double sumOfSmoothingParams = (numAttributes-1)*smoothingParameter;
int classIndex = instances.instance(0).classIndex();
Instance instance;
int docClass;
double numOccurrences;
java.util.Enumeration enumInsts = instances.enumerateInstances();
while (enumInsts.hasMoreElements()) {
instance = (Instance) enumInsts.nextElement();
docClass = (int)instance.value(classIndex);
//docsPerClass[docClass] += instance.weight();
for(int a = 0; a<instance.numValues(); a++)
if(instance.index(a) != instance.classIndex()) {
if(!instance.isMissing(a)) {
numOccurrences = instance.valueSparse(a) * instance.weight();
if(numOccurrences < 0)
throw new Exception("Numeric attribute"+
" values must all be greater"+
" or equal to zero.");
totalWordOccurrences += numOccurrences;
wordsPerClass[docClass] += numOccurrences;
ocrnceOfWordInClass[docClass]
[instance.index(a)] += numOccurrences;
//For the time being wordweights[0][i]
//will hold the total occurrence of word
// i over all classes
wordWeights[0]
[instance.index(a)] += numOccurrences;
}
}
}
//Calculating the complement class probability for all classes except 0
for(int c=1; c<numClasses; c++) {
//total occurrence of words in classes other than c
double totalWordOcrnces = totalWordOccurrences - wordsPerClass[c];
for(int w=0; w<numAttributes; w++) {
if(w != classIndex ) {
//occurrence of w in classes other that c
double ocrncesOfWord =
wordWeights[0][w] - ocrnceOfWordInClass[c][w];
wordWeights[c][w] =
Math.log((ocrncesOfWord+smoothingParameter) /
(totalWordOcrnces+sumOfSmoothingParams));
}
}
}
//Now calculating the complement class probability for class 0
for(int w=0; w<numAttributes; w++) {
if(w != classIndex) {
//occurrence of w in classes other that c
double ocrncesOfWord = wordWeights[0][w] - ocrnceOfWordInClass[0][w];
//total occurrence of words in classes other than c
double totalWordOcrnces = totalWordOccurrences - wordsPerClass[0];
wordWeights[0][w] =
Math.log((ocrncesOfWord+smoothingParameter) /
(totalWordOcrnces+sumOfSmoothingParams));
}
}
//Normalizing weights
if(m_normalizeWordWeights==true)
for(int c=0; c<numClasses; c++) {
double sum=0;
for(int w=0; w<numAttributes; w++) {
if(w!=classIndex)
sum += Math.abs(wordWeights[c][w]);
}
for(int w=0; w<numAttributes; w++) {
if(w!=classIndex) {
wordWeights[c][w] = wordWeights[c][w]/sum;
}
}
}
}
/**
* Classifies a given instance. <p>
*
* The classification rule is: <br>
* MinC(forAllWords(ti*Wci)) <br>
* where <br>
* ti is the frequency of word i in the given instance <br>
* Wci is the weight of word i in Class c. <p>
*
* For more information see section 4.4 of the paper mentioned above
* in the classifiers description.
*
* @param instance the instance to classify
* @return the index of the class the instance is most likely to belong.
* @throws Exception if the classifier has not been built yet.
*/
public double classifyInstance(Instance instance) throws Exception {
if(wordWeights==null)
throw new Exception("Error. The classifier has not been built "+
"properly.");
double [] valueForClass = new double[numClasses];
double sumOfClassValues=0;
for(int c=0; c<numClasses; c++) {
double sumOfWordValues=0;
for(int w=0; w<instance.numValues(); w++) {
if(instance.index(w)!=instance.classIndex()) {
double freqOfWordInDoc = instance.valueSparse(w);
sumOfWordValues += freqOfWordInDoc *
wordWeights[c][instance.index(w)];
}
}
//valueForClass[c] = Math.log(probOfClass[c]) - sumOfWordValues;
valueForClass[c] = sumOfWordValues;
sumOfClassValues += valueForClass[c];
}
int minidx=0;
for(int i=0; i<numClasses; i++)
if(valueForClass[i]<valueForClass[minidx])
minidx = i;
return minidx;
}
/**
* Prints out the internal model built by the classifier. In this case
* it prints out the word weights calculated when building the classifier.
*/
public String toString() {
if(wordWeights==null) {
return "The classifier hasn't been built yet.";
}
int numAttributes = header.numAttributes();
StringBuffer result = new StringBuffer("The word weights for each class are: \n"+
"------------------------------------\n\t");
for(int c = 0; c<numClasses; c++)
result.append(header.classAttribute().value(c)).append("\t");
result.append("\n");
for(int w = 0; w<numAttributes; w++) {
result.append(header.attribute(w).name()).append("\t");
for(int c = 0; c<numClasses; c++)
result.append(Double.toString(wordWeights[c][w])).append("\t");
result.append("\n");
}
return result.toString();
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 1.9 $");
}
/**
* Main method for testing this class.
*
* @param argv the options
*/
public static void main(String [] argv) {
runClassifier(new ComplementNaiveBayes(), argv);
}
}