/*
* RapidMiner
*
* Copyright (C) 2001-2008 by Rapid-I and the contributors
*
* Complete list of developers available at our web site:
*
* http://rapid-i.com
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see http://www.gnu.org/licenses/.
*/
package com.rapidminer.operator.learner.meta;
import java.util.Iterator;
import com.rapidminer.example.Attribute;
import com.rapidminer.example.Example;
import com.rapidminer.example.ExampleSet;
import com.rapidminer.operator.OperatorException;
/**
* Helper class for the internal AdaBoost implementation.
*
* @author Martin Scholz
* @version $Id: AdaBoostPerformanceMeasures.java,v 1.3 2006/04/14 15:04:22
* ingomierswa Exp $
*/
public class AdaBoostPerformanceMeasures extends WeightedPerformanceMeasures {
private final double errorRate;
/**
* @param exampleSet
* @throws OperatorException
*/
public AdaBoostPerformanceMeasures(ExampleSet exampleSet) throws OperatorException {
super(exampleSet);
int num = this.getNumberOfLabels();
double correct = 0;
for (int i = 0; i < num; i++) {
correct += this.getProbability(i, i);
}
this.errorRate = Math.max(0, Math.min(1, 1.0d - correct));
}
/** @return the error rate computed by the constructor */
public double getErrorRate() {
return this.errorRate;
}
/**
* This method reweights the example set with respect to the performance
* measures. Please note that the weights will not be reset at any time,
* because they continuously change from one iteration to the next.
*
* @param exampleSet
* <code>ExampleSet</code> to be reweighted
* @return the total weight after reweighting.
*/
public double reweightExamples(ExampleSet exampleSet) throws OperatorException {
double reweightRightPred, reweightWrongPred;
final double err = this.getErrorRate();
if (err == 0 || err == 1) {
reweightRightPred = 1;
reweightWrongPred = 1;
} else {
reweightRightPred = Math.sqrt(err / (1.0d - err));
reweightWrongPred = 1.0d / reweightRightPred;
}
double totalWeight = 0;
Iterator<Example> reader = exampleSet.iterator();
Attribute weightAttribute = exampleSet.getAttributes().getWeight();
while (reader.hasNext()) {
Example example = reader.next();
int label = (int) example.getLabel();
int predicted = (int) example.getPredictedLabel();
double newWeight = example.getValue(weightAttribute) * ((label == predicted) ? reweightRightPred : reweightWrongPred);
example.setValue(weightAttribute, newWeight);
totalWeight += newWeight;
}
return totalWeight;
}
}