/*
* 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.
*/
/*
* LogitBoost.java
* Copyright (C) 1999, 2002 University of Waikato, Hamilton, New Zealand
*
*/
package weka.classifiers.meta;
import weka.classifiers.Classifier;
import weka.classifiers.Evaluation;
import weka.classifiers.RandomizableIteratedSingleClassifierEnhancer;
import weka.classifiers.Sourcable;
import weka.core.Attribute;
import weka.core.Capabilities;
import weka.core.Instance;
import weka.core.Instances;
import weka.core.Option;
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;
import java.util.Enumeration;
import java.util.Random;
import java.util.Vector;
/**
<!-- globalinfo-start -->
* Class for performing additive logistic regression. <br/>
* This class performs classification using a regression scheme as the base learner, and can handle multi-class problems. For more information, see<br/>
* <br/>
* J. Friedman, T. Hastie, R. Tibshirani (1998). Additive Logistic Regression: a Statistical View of Boosting. Stanford University.<br/>
* <br/>
* Can do efficient internal cross-validation to determine appropriate number of iterations.
* <p/>
<!-- globalinfo-end -->
*
<!-- technical-bibtex-start -->
* BibTeX:
* <pre>
* @techreport{Friedman1998,
* address = {Stanford University},
* author = {J. Friedman and T. Hastie and R. Tibshirani},
* title = {Additive Logistic Regression: a Statistical View of Boosting},
* year = {1998},
* PS = {http://www-stat.stanford.edu/\~jhf/ftp/boost.ps}
* }
* </pre>
* <p/>
<!-- technical-bibtex-end -->
*
<!-- options-start -->
* Valid options are: <p/>
*
* <pre> -Q
* Use resampling instead of reweighting for boosting.</pre>
*
* <pre> -P <percent>
* Percentage of weight mass to base training on.
* (default 100, reduce to around 90 speed up)</pre>
*
* <pre> -F <num>
* Number of folds for internal cross-validation.
* (default 0 -- no cross-validation)</pre>
*
* <pre> -R <num>
* Number of runs for internal cross-validation.
* (default 1)</pre>
*
* <pre> -L <num>
* Threshold on the improvement of the likelihood.
* (default -Double.MAX_VALUE)</pre>
*
* <pre> -H <num>
* Shrinkage parameter.
* (default 1)</pre>
*
* <pre> -S <num>
* Random number seed.
* (default 1)</pre>
*
* <pre> -I <num>
* Number of iterations.
* (default 10)</pre>
*
* <pre> -D
* If set, classifier is run in debug mode and
* may output additional info to the console</pre>
*
* <pre> -W
* Full name of base classifier.
* (default: weka.classifiers.trees.DecisionStump)</pre>
*
* <pre>
* Options specific to classifier weka.classifiers.trees.DecisionStump:
* </pre>
*
* <pre> -D
* If set, classifier is run in debug mode and
* may output additional info to the console</pre>
*
<!-- options-end -->
*
* Options after -- are passed to the designated learner.<p>
*
* @author Len Trigg (trigg@cs.waikato.ac.nz)
* @author Eibe Frank (eibe@cs.waikato.ac.nz)
* @version $Revision: 1.43 $
*/
public class LogitBoost
extends RandomizableIteratedSingleClassifierEnhancer
implements Sourcable, WeightedInstancesHandler, TechnicalInformationHandler {
/** for serialization */
static final long serialVersionUID = -3905660358715833753L;
/** Array for storing the generated base classifiers.
Note: we are hiding the variable from IteratedSingleClassifierEnhancer*/
protected Classifier [][] m_Classifiers;
/** The number of classes */
protected int m_NumClasses;
/** The number of successfully generated base classifiers. */
protected int m_NumGenerated;
/** The number of folds for the internal cross-validation. */
protected int m_NumFolds = 0;
/** The number of runs for the internal cross-validation. */
protected int m_NumRuns = 1;
/** Weight thresholding. The percentage of weight mass used in training */
protected int m_WeightThreshold = 100;
/** A threshold for responses (Friedman suggests between 2 and 4) */
protected static final double Z_MAX = 3;
/** Dummy dataset with a numeric class */
protected Instances m_NumericClassData;
/** The actual class attribute (for getting class names) */
protected Attribute m_ClassAttribute;
/** Use boosting with reweighting? */
protected boolean m_UseResampling;
/** The threshold on the improvement of the likelihood */
protected double m_Precision = -Double.MAX_VALUE;
/** The value of the shrinkage parameter */
protected double m_Shrinkage = 1;
/** The random number generator used */
protected Random m_RandomInstance = null;
/** The value by which the actual target value for the
true class is offset. */
protected double m_Offset = 0.0;
/** a ZeroR model in case no model can be built from the data */
protected Classifier m_ZeroR;
/**
* Returns a string describing classifier
* @return a description suitable for
* displaying in the explorer/experimenter gui
*/
public String globalInfo() {
return "Class for performing additive logistic regression. \n"
+ "This class performs classification using a regression scheme as the "
+ "base learner, and can handle multi-class problems. For more "
+ "information, see\n\n"
+ getTechnicalInformation().toString() + "\n\n"
+ "Can do efficient internal cross-validation to determine "
+ "appropriate number of iterations.";
}
/**
* Constructor.
*/
public LogitBoost() {
m_Classifier = new weka.classifiers.trees.DecisionStump();
}
/**
* 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.TECHREPORT);
result.setValue(Field.AUTHOR, "J. Friedman and T. Hastie and R. Tibshirani");
result.setValue(Field.YEAR, "1998");
result.setValue(Field.TITLE, "Additive Logistic Regression: a Statistical View of Boosting");
result.setValue(Field.ADDRESS, "Stanford University");
result.setValue(Field.PS, "http://www-stat.stanford.edu/~jhf/ftp/boost.ps");
return result;
}
/**
* String describing default classifier.
*
* @return the default classifier classname
*/
protected String defaultClassifierString() {
return "weka.classifiers.trees.DecisionStump";
}
/**
* Select only instances with weights that contribute to
* the specified quantile of the weight distribution
*
* @param data the input instances
* @param quantile the specified quantile eg 0.9 to select
* 90% of the weight mass
* @return the selected instances
*/
protected Instances selectWeightQuantile(Instances data, double quantile) {
int numInstances = data.numInstances();
Instances trainData = new Instances(data, numInstances);
double [] weights = new double [numInstances];
double sumOfWeights = 0;
for (int i = 0; i < numInstances; i++) {
weights[i] = data.instance(i).weight();
sumOfWeights += weights[i];
}
double weightMassToSelect = sumOfWeights * quantile;
int [] sortedIndices = Utils.sort(weights);
// Select the instances
sumOfWeights = 0;
for (int i = numInstances-1; i >= 0; i--) {
Instance instance = (Instance)data.instance(sortedIndices[i]).copy();
trainData.add(instance);
sumOfWeights += weights[sortedIndices[i]];
if ((sumOfWeights > weightMassToSelect) &&
(i > 0) &&
(weights[sortedIndices[i]] != weights[sortedIndices[i-1]])) {
break;
}
}
if (m_Debug) {
System.err.println("Selected " + trainData.numInstances()
+ " out of " + numInstances);
}
return trainData;
}
/**
* Returns an enumeration describing the available options.
*
* @return an enumeration of all the available options.
*/
public Enumeration listOptions() {
Vector newVector = new Vector(6);
newVector.addElement(new Option(
"\tUse resampling instead of reweighting for boosting.",
"Q", 0, "-Q"));
newVector.addElement(new Option(
"\tPercentage of weight mass to base training on.\n"
+"\t(default 100, reduce to around 90 speed up)",
"P", 1, "-P <percent>"));
newVector.addElement(new Option(
"\tNumber of folds for internal cross-validation.\n"
+"\t(default 0 -- no cross-validation)",
"F", 1, "-F <num>"));
newVector.addElement(new Option(
"\tNumber of runs for internal cross-validation.\n"
+"\t(default 1)",
"R", 1, "-R <num>"));
newVector.addElement(new Option(
"\tThreshold on the improvement of the likelihood.\n"
+"\t(default -Double.MAX_VALUE)",
"L", 1, "-L <num>"));
newVector.addElement(new Option(
"\tShrinkage parameter.\n"
+"\t(default 1)",
"H", 1, "-H <num>"));
Enumeration enu = super.listOptions();
while (enu.hasMoreElements()) {
newVector.addElement(enu.nextElement());
}
return newVector.elements();
}
/**
* Parses a given list of options. <p/>
*
<!-- options-start -->
* Valid options are: <p/>
*
* <pre> -Q
* Use resampling instead of reweighting for boosting.</pre>
*
* <pre> -P <percent>
* Percentage of weight mass to base training on.
* (default 100, reduce to around 90 speed up)</pre>
*
* <pre> -F <num>
* Number of folds for internal cross-validation.
* (default 0 -- no cross-validation)</pre>
*
* <pre> -R <num>
* Number of runs for internal cross-validation.
* (default 1)</pre>
*
* <pre> -L <num>
* Threshold on the improvement of the likelihood.
* (default -Double.MAX_VALUE)</pre>
*
* <pre> -H <num>
* Shrinkage parameter.
* (default 1)</pre>
*
* <pre> -S <num>
* Random number seed.
* (default 1)</pre>
*
* <pre> -I <num>
* Number of iterations.
* (default 10)</pre>
*
* <pre> -D
* If set, classifier is run in debug mode and
* may output additional info to the console</pre>
*
* <pre> -W
* Full name of base classifier.
* (default: weka.classifiers.trees.DecisionStump)</pre>
*
* <pre>
* Options specific to classifier weka.classifiers.trees.DecisionStump:
* </pre>
*
* <pre> -D
* If set, classifier is run in debug mode and
* may output additional info to the console</pre>
*
<!-- options-end -->
*
* Options after -- are passed to the designated learner.<p>
*
* @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 {
String numFolds = Utils.getOption('F', options);
if (numFolds.length() != 0) {
setNumFolds(Integer.parseInt(numFolds));
} else {
setNumFolds(0);
}
String numRuns = Utils.getOption('R', options);
if (numRuns.length() != 0) {
setNumRuns(Integer.parseInt(numRuns));
} else {
setNumRuns(1);
}
String thresholdString = Utils.getOption('P', options);
if (thresholdString.length() != 0) {
setWeightThreshold(Integer.parseInt(thresholdString));
} else {
setWeightThreshold(100);
}
String precisionString = Utils.getOption('L', options);
if (precisionString.length() != 0) {
setLikelihoodThreshold(new Double(precisionString).
doubleValue());
} else {
setLikelihoodThreshold(-Double.MAX_VALUE);
}
String shrinkageString = Utils.getOption('H', options);
if (shrinkageString.length() != 0) {
setShrinkage(new Double(shrinkageString).
doubleValue());
} else {
setShrinkage(1.0);
}
setUseResampling(Utils.getFlag('Q', options));
if (m_UseResampling && (thresholdString.length() != 0)) {
throw new Exception("Weight pruning with resampling"+
"not allowed.");
}
super.setOptions(options);
}
/**
* Gets the current settings of the Classifier.
*
* @return an array of strings suitable for passing to setOptions
*/
public String [] getOptions() {
String [] superOptions = super.getOptions();
String [] options = new String [superOptions.length + 10];
int current = 0;
if (getUseResampling()) {
options[current++] = "-Q";
} else {
options[current++] = "-P";
options[current++] = "" + getWeightThreshold();
}
options[current++] = "-F"; options[current++] = "" + getNumFolds();
options[current++] = "-R"; options[current++] = "" + getNumRuns();
options[current++] = "-L"; options[current++] = "" + getLikelihoodThreshold();
options[current++] = "-H"; options[current++] = "" + getShrinkage();
System.arraycopy(superOptions, 0, options, current,
superOptions.length);
current += superOptions.length;
while (current < options.length) {
options[current++] = "";
}
return options;
}
/**
* Returns the tip text for this property
* @return tip text for this property suitable for
* displaying in the explorer/experimenter gui
*/
public String shrinkageTipText() {
return "Shrinkage parameter (use small value like 0.1 to reduce "
+ "overfitting).";
}
/**
* Get the value of Shrinkage.
*
* @return Value of Shrinkage.
*/
public double getShrinkage() {
return m_Shrinkage;
}
/**
* Set the value of Shrinkage.
*
* @param newShrinkage Value to assign to Shrinkage.
*/
public void setShrinkage(double newShrinkage) {
m_Shrinkage = newShrinkage;
}
/**
* Returns the tip text for this property
* @return tip text for this property suitable for
* displaying in the explorer/experimenter gui
*/
public String likelihoodThresholdTipText() {
return "Threshold on improvement in likelihood.";
}
/**
* Get the value of Precision.
*
* @return Value of Precision.
*/
public double getLikelihoodThreshold() {
return m_Precision;
}
/**
* Set the value of Precision.
*
* @param newPrecision Value to assign to Precision.
*/
public void setLikelihoodThreshold(double newPrecision) {
m_Precision = newPrecision;
}
/**
* Returns the tip text for this property
* @return tip text for this property suitable for
* displaying in the explorer/experimenter gui
*/
public String numRunsTipText() {
return "Number of runs for internal cross-validation.";
}
/**
* Get the value of NumRuns.
*
* @return Value of NumRuns.
*/
public int getNumRuns() {
return m_NumRuns;
}
/**
* Set the value of NumRuns.
*
* @param newNumRuns Value to assign to NumRuns.
*/
public void setNumRuns(int newNumRuns) {
m_NumRuns = newNumRuns;
}
/**
* Returns the tip text for this property
* @return tip text for this property suitable for
* displaying in the explorer/experimenter gui
*/
public String numFoldsTipText() {
return "Number of folds for internal cross-validation (default 0 "
+ "means no cross-validation is performed).";
}
/**
* Get the value of NumFolds.
*
* @return Value of NumFolds.
*/
public int getNumFolds() {
return m_NumFolds;
}
/**
* Set the value of NumFolds.
*
* @param newNumFolds Value to assign to NumFolds.
*/
public void setNumFolds(int newNumFolds) {
m_NumFolds = newNumFolds;
}
/**
* Returns the tip text for this property
* @return tip text for this property suitable for
* displaying in the explorer/experimenter gui
*/
public String useResamplingTipText() {
return "Whether resampling is used instead of reweighting.";
}
/**
* Set resampling mode
*
* @param r true if resampling should be done
*/
public void setUseResampling(boolean r) {
m_UseResampling = r;
}
/**
* Get whether resampling is turned on
*
* @return true if resampling output is on
*/
public boolean getUseResampling() {
return m_UseResampling;
}
/**
* Returns the tip text for this property
* @return tip text for this property suitable for
* displaying in the explorer/experimenter gui
*/
public String weightThresholdTipText() {
return "Weight threshold for weight pruning (reduce to 90 "
+ "for speeding up learning process).";
}
/**
* Set weight thresholding
*
* @param threshold the percentage of weight mass used for training
*/
public void setWeightThreshold(int threshold) {
m_WeightThreshold = threshold;
}
/**
* Get the degree of weight thresholding
*
* @return the percentage of weight mass used for training
*/
public int getWeightThreshold() {
return m_WeightThreshold;
}
/**
* Returns default capabilities of the classifier.
*
* @return the capabilities of this classifier
*/
public Capabilities getCapabilities() {
Capabilities result = super.getCapabilities();
// class
result.disableAllClasses();
result.disableAllClassDependencies();
result.enable(Capability.NOMINAL_CLASS);
return result;
}
/**
* Builds the boosted classifier
*
* @param data the data to train the classifier with
* @throws Exception if building fails, e.g., can't handle data
*/
public void buildClassifier(Instances data) throws Exception {
m_RandomInstance = new Random(m_Seed);
int classIndex = data.classIndex();
if (m_Classifier == null) {
throw new Exception("A base classifier has not been specified!");
}
if (!(m_Classifier instanceof WeightedInstancesHandler) &&
!m_UseResampling) {
m_UseResampling = true;
}
// can classifier handle the data?
getCapabilities().testWithFail(data);
if (m_Debug) {
System.err.println("Creating copy of the training data");
}
// remove instances with missing class
data = new Instances(data);
data.deleteWithMissingClass();
// only class? -> build ZeroR model
if (data.numAttributes() == 1) {
System.err.println(
"Cannot build model (only class attribute present in data!), "
+ "using ZeroR model instead!");
m_ZeroR = new weka.classifiers.rules.ZeroR();
m_ZeroR.buildClassifier(data);
return;
}
else {
m_ZeroR = null;
}
m_NumClasses = data.numClasses();
m_ClassAttribute = data.classAttribute();
// Create the base classifiers
if (m_Debug) {
System.err.println("Creating base classifiers");
}
m_Classifiers = new Classifier [m_NumClasses][];
for (int j = 0; j < m_NumClasses; j++) {
m_Classifiers[j] = Classifier.makeCopies(m_Classifier,
getNumIterations());
}
// Do we want to select the appropriate number of iterations
// using cross-validation?
int bestNumIterations = getNumIterations();
if (m_NumFolds > 1) {
if (m_Debug) {
System.err.println("Processing first fold.");
}
// Array for storing the results
double[] results = new double[getNumIterations()];
// Iterate throught the cv-runs
for (int r = 0; r < m_NumRuns; r++) {
// Stratify the data
data.randomize(m_RandomInstance);
data.stratify(m_NumFolds);
// Perform the cross-validation
for (int i = 0; i < m_NumFolds; i++) {
// Get train and test folds
Instances train = data.trainCV(m_NumFolds, i, m_RandomInstance);
Instances test = data.testCV(m_NumFolds, i);
// Make class numeric
Instances trainN = new Instances(train);
trainN.setClassIndex(-1);
trainN.deleteAttributeAt(classIndex);
trainN.insertAttributeAt(new Attribute("'pseudo class'"), classIndex);
trainN.setClassIndex(classIndex);
m_NumericClassData = new Instances(trainN, 0);
// Get class values
int numInstances = train.numInstances();
double [][] trainFs = new double [numInstances][m_NumClasses];
double [][] trainYs = new double [numInstances][m_NumClasses];
for (int j = 0; j < m_NumClasses; j++) {
for (int k = 0; k < numInstances; k++) {
trainYs[k][j] = (train.instance(k).classValue() == j) ?
1.0 - m_Offset: 0.0 + (m_Offset / (double)m_NumClasses);
}
}
// Perform iterations
double[][] probs = initialProbs(numInstances);
m_NumGenerated = 0;
double sumOfWeights = train.sumOfWeights();
for (int j = 0; j < getNumIterations(); j++) {
performIteration(trainYs, trainFs, probs, trainN, sumOfWeights);
Evaluation eval = new Evaluation(train);
eval.evaluateModel(this, test);
results[j] += eval.correct();
}
}
}
// Find the number of iterations with the lowest error
double bestResult = -Double.MAX_VALUE;
for (int j = 0; j < getNumIterations(); j++) {
if (results[j] > bestResult) {
bestResult = results[j];
bestNumIterations = j;
}
}
if (m_Debug) {
System.err.println("Best result for " +
bestNumIterations + " iterations: " +
bestResult);
}
}
// Build classifier on all the data
int numInstances = data.numInstances();
double [][] trainFs = new double [numInstances][m_NumClasses];
double [][] trainYs = new double [numInstances][m_NumClasses];
for (int j = 0; j < m_NumClasses; j++) {
for (int i = 0, k = 0; i < numInstances; i++, k++) {
trainYs[i][j] = (data.instance(k).classValue() == j) ?
1.0 - m_Offset: 0.0 + (m_Offset / (double)m_NumClasses);
}
}
// Make class numeric
data.setClassIndex(-1);
data.deleteAttributeAt(classIndex);
data.insertAttributeAt(new Attribute("'pseudo class'"), classIndex);
data.setClassIndex(classIndex);
m_NumericClassData = new Instances(data, 0);
// Perform iterations
double[][] probs = initialProbs(numInstances);
double logLikelihood = logLikelihood(trainYs, probs);
m_NumGenerated = 0;
if (m_Debug) {
System.err.println("Avg. log-likelihood: " + logLikelihood);
}
double sumOfWeights = data.sumOfWeights();
for (int j = 0; j < bestNumIterations; j++) {
double previousLoglikelihood = logLikelihood;
performIteration(trainYs, trainFs, probs, data, sumOfWeights);
logLikelihood = logLikelihood(trainYs, probs);
if (m_Debug) {
System.err.println("Avg. log-likelihood: " + logLikelihood);
}
if (Math.abs(previousLoglikelihood - logLikelihood) < m_Precision) {
return;
}
}
}
/**
* Gets the intial class probabilities.
*
* @param numInstances the number of instances
* @return the initial class probabilities
*/
private double[][] initialProbs(int numInstances) {
double[][] probs = new double[numInstances][m_NumClasses];
for (int i = 0; i < numInstances; i++) {
for (int j = 0 ; j < m_NumClasses; j++) {
probs[i][j] = 1.0 / m_NumClasses;
}
}
return probs;
}
/**
* Computes loglikelihood given class values
* and estimated probablities.
*
* @param trainYs class values
* @param probs estimated probabilities
* @return the computed loglikelihood
*/
private double logLikelihood(double[][] trainYs, double[][] probs) {
double logLikelihood = 0;
for (int i = 0; i < trainYs.length; i++) {
for (int j = 0; j < m_NumClasses; j++) {
if (trainYs[i][j] == 1.0 - m_Offset) {
logLikelihood -= Math.log(probs[i][j]);
}
}
}
return logLikelihood / (double)trainYs.length;
}
/**
* Performs one boosting iteration.
*
* @param trainYs class values
* @param trainFs F scores
* @param probs probabilities
* @param data the data to run the iteration on
* @param origSumOfWeights the original sum of weights
* @throws Exception in case base classifiers run into problems
*/
private void performIteration(double[][] trainYs,
double[][] trainFs,
double[][] probs,
Instances data,
double origSumOfWeights) throws Exception {
if (m_Debug) {
System.err.println("Training classifier " + (m_NumGenerated + 1));
}
// Build the new models
for (int j = 0; j < m_NumClasses; j++) {
if (m_Debug) {
System.err.println("\t...for class " + (j + 1)
+ " (" + m_ClassAttribute.name()
+ "=" + m_ClassAttribute.value(j) + ")");
}
// Make copy because we want to save the weights
Instances boostData = new Instances(data);
// Set instance pseudoclass and weights
for (int i = 0; i < probs.length; i++) {
// Compute response and weight
double p = probs[i][j];
double z, actual = trainYs[i][j];
if (actual == 1 - m_Offset) {
z = 1.0 / p;
if (z > Z_MAX) { // threshold
z = Z_MAX;
}
} else {
z = -1.0 / (1.0 - p);
if (z < -Z_MAX) { // threshold
z = -Z_MAX;
}
}
double w = (actual - p) / z;
// Set values for instance
Instance current = boostData.instance(i);
current.setValue(boostData.classIndex(), z);
current.setWeight(current.weight() * w);
}
// Scale the weights (helps with some base learners)
double sumOfWeights = boostData.sumOfWeights();
double scalingFactor = (double)origSumOfWeights / sumOfWeights;
for (int i = 0; i < probs.length; i++) {
Instance current = boostData.instance(i);
current.setWeight(current.weight() * scalingFactor);
}
// Select instances to train the classifier on
Instances trainData = boostData;
if (m_WeightThreshold < 100) {
trainData = selectWeightQuantile(boostData,
(double)m_WeightThreshold / 100);
} else {
if (m_UseResampling) {
double[] weights = new double[boostData.numInstances()];
for (int kk = 0; kk < weights.length; kk++) {
weights[kk] = boostData.instance(kk).weight();
}
trainData = boostData.resampleWithWeights(m_RandomInstance,
weights);
}
}
// Build the classifier
m_Classifiers[j][m_NumGenerated].buildClassifier(trainData);
}
// Evaluate / increment trainFs from the classifier
for (int i = 0; i < trainFs.length; i++) {
double [] pred = new double [m_NumClasses];
double predSum = 0;
for (int j = 0; j < m_NumClasses; j++) {
pred[j] = m_Shrinkage * m_Classifiers[j][m_NumGenerated]
.classifyInstance(data.instance(i));
predSum += pred[j];
}
predSum /= m_NumClasses;
for (int j = 0; j < m_NumClasses; j++) {
trainFs[i][j] += (pred[j] - predSum) * (m_NumClasses - 1)
/ m_NumClasses;
}
}
m_NumGenerated++;
// Compute the current probability estimates
for (int i = 0; i < trainYs.length; i++) {
probs[i] = probs(trainFs[i]);
}
}
/**
* Returns the array of classifiers that have been built.
*
* @return the built classifiers
*/
public Classifier[][] classifiers() {
Classifier[][] classifiers =
new Classifier[m_NumClasses][m_NumGenerated];
for (int j = 0; j < m_NumClasses; j++) {
for (int i = 0; i < m_NumGenerated; i++) {
classifiers[j][i] = m_Classifiers[j][i];
}
}
return classifiers;
}
/**
* Computes probabilities from F scores
*
* @param Fs the F scores
* @return the computed probabilities
*/
private double[] probs(double[] Fs) {
double maxF = -Double.MAX_VALUE;
for (int i = 0; i < Fs.length; i++) {
if (Fs[i] > maxF) {
maxF = Fs[i];
}
}
double sum = 0;
double[] probs = new double[Fs.length];
for (int i = 0; i < Fs.length; i++) {
probs[i] = Math.exp(Fs[i] - maxF);
sum += probs[i];
}
Utils.normalize(probs, sum);
return probs;
}
/**
* 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 instance could not be classified
* successfully
*/
public double [] distributionForInstance(Instance instance)
throws Exception {
// default model?
if (m_ZeroR != null) {
return m_ZeroR.distributionForInstance(instance);
}
instance = (Instance)instance.copy();
instance.setDataset(m_NumericClassData);
double [] pred = new double [m_NumClasses];
double [] Fs = new double [m_NumClasses];
for (int i = 0; i < m_NumGenerated; i++) {
double predSum = 0;
for (int j = 0; j < m_NumClasses; j++) {
pred[j] = m_Classifiers[j][i].classifyInstance(instance);
predSum += pred[j];
}
predSum /= m_NumClasses;
for (int j = 0; j < m_NumClasses; j++) {
Fs[j] += (pred[j] - predSum) * (m_NumClasses - 1)
/ m_NumClasses;
}
}
return probs(Fs);
}
/**
* Returns the boosted model as Java source code.
*
* @param className the classname in the generated code
* @return the tree as Java source code
* @throws Exception if something goes wrong
*/
public String toSource(String className) throws Exception {
if (m_NumGenerated == 0) {
throw new Exception("No model built yet");
}
if (!(m_Classifiers[0][0] instanceof Sourcable)) {
throw new Exception("Base learner " + m_Classifier.getClass().getName()
+ " is not Sourcable");
}
StringBuffer text = new StringBuffer("class ");
text.append(className).append(" {\n\n");
text.append(" private static double RtoP(double []R, int j) {\n"+
" double Rcenter = 0;\n"+
" for (int i = 0; i < R.length; i++) {\n"+
" Rcenter += R[i];\n"+
" }\n"+
" Rcenter /= R.length;\n"+
" double Rsum = 0;\n"+
" for (int i = 0; i < R.length; i++) {\n"+
" Rsum += Math.exp(R[i] - Rcenter);\n"+
" }\n"+
" return Math.exp(R[j]) / Rsum;\n"+
" }\n\n");
text.append(" public static double classify(Object[] i) {\n" +
" double [] d = distribution(i);\n" +
" double maxV = d[0];\n" +
" int maxI = 0;\n"+
" for (int j = 1; j < " + m_NumClasses + "; j++) {\n"+
" if (d[j] > maxV) { maxV = d[j]; maxI = j; }\n"+
" }\n return (double) maxI;\n }\n\n");
text.append(" public static double [] distribution(Object [] i) {\n");
text.append(" double [] Fs = new double [" + m_NumClasses + "];\n");
text.append(" double [] Fi = new double [" + m_NumClasses + "];\n");
text.append(" double Fsum;\n");
for (int i = 0; i < m_NumGenerated; i++) {
text.append(" Fsum = 0;\n");
for (int j = 0; j < m_NumClasses; j++) {
text.append(" Fi[" + j + "] = " + className + '_' +j + '_' + i
+ ".classify(i); Fsum += Fi[" + j + "];\n");
}
text.append(" Fsum /= " + m_NumClasses + ";\n");
text.append(" for (int j = 0; j < " + m_NumClasses + "; j++) {");
text.append(" Fs[j] += (Fi[j] - Fsum) * "
+ (m_NumClasses - 1) + " / " + m_NumClasses + "; }\n");
}
text.append(" double [] dist = new double [" + m_NumClasses + "];\n" +
" for (int j = 0; j < " + m_NumClasses + "; j++) {\n"+
" dist[j] = RtoP(Fs, j);\n"+
" }\n return dist;\n");
text.append(" }\n}\n");
for (int i = 0; i < m_Classifiers.length; i++) {
for (int j = 0; j < m_Classifiers[i].length; j++) {
text.append(((Sourcable)m_Classifiers[i][j])
.toSource(className + '_' + i + '_' + j));
}
}
return text.toString();
}
/**
* Returns description of the boosted classifier.
*
* @return description of the boosted classifier as a string
*/
public String toString() {
// only ZeroR model?
if (m_ZeroR != null) {
StringBuffer buf = new StringBuffer();
buf.append(this.getClass().getName().replaceAll(".*\\.", "") + "\n");
buf.append(this.getClass().getName().replaceAll(".*\\.", "").replaceAll(".", "=") + "\n\n");
buf.append("Warning: No model could be built, hence ZeroR model is used:\n\n");
buf.append(m_ZeroR.toString());
return buf.toString();
}
StringBuffer text = new StringBuffer();
if (m_NumGenerated == 0) {
text.append("LogitBoost: No model built yet.");
// text.append(m_Classifiers[0].toString()+"\n");
} else {
text.append("LogitBoost: Base classifiers and their weights: \n");
for (int i = 0; i < m_NumGenerated; i++) {
text.append("\nIteration "+(i+1));
for (int j = 0; j < m_NumClasses; j++) {
text.append("\n\tClass " + (j + 1)
+ " (" + m_ClassAttribute.name()
+ "=" + m_ClassAttribute.value(j) + ")\n\n"
+ m_Classifiers[j][i].toString() + "\n");
}
}
text.append("Number of performed iterations: " +
m_NumGenerated + "\n");
}
return text.toString();
}
/**
* Returns the revision string.
*
* @return the revision
*/
public String getRevision() {
return RevisionUtils.extract("$Revision: 1.43 $");
}
/**
* Main method for testing this class.
*
* @param argv the options
*/
public static void main(String [] argv) {
runClassifier(new LogitBoost(), argv);
}
}