/*
* 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.tree;
import java.util.Iterator;
import java.util.List;
import com.rapidminer.example.Attribute;
import com.rapidminer.example.AttributeWeights;
import com.rapidminer.example.ExampleSet;
import com.rapidminer.operator.IOContainer;
import com.rapidminer.operator.Operator;
import com.rapidminer.operator.OperatorCreationException;
import com.rapidminer.operator.OperatorDescription;
import com.rapidminer.operator.OperatorException;
import com.rapidminer.operator.features.weighting.ChiSquaredWeighting;
import com.rapidminer.parameter.ParameterType;
import com.rapidminer.tools.OperatorService;
/**
* The CHAID decision tree learner works like the
* {@link com.rapidminer.operator.learner.tree.DecisionTreeLearner}
* with one exception: it used a chi squared based criterion
* instead of the information gain or gain ratio criteria.
*
* @author Ingo Mierswa
* @version $Id: CHAIDLearner.java,v 1.4 2008/05/09 19:22:52 ingomierswa Exp $
*/
public class CHAIDLearner extends DecisionTreeLearner {
public CHAIDLearner(OperatorDescription description) {
super(description);
}
/** This method calculates the benefit of the given attribute. This implementation
* utilizes the defined {@link Criterion}. Subclasses might want to override this
* method in order to calculate the benefit in other ways. */
protected Benefit calculateBenefit(ExampleSet trainingSet, Attribute attribute) throws OperatorException {
Operator weightOp = null;
try {
weightOp = OperatorService.createOperator(ChiSquaredWeighting.class);
} catch (OperatorCreationException e) {
logWarning("Cannot create chi squared calculation operator.");
}
double weight = Double.NaN;
if (weightOp != null) {
IOContainer output = weightOp.apply(new IOContainer(trainingSet));
AttributeWeights weights = output.remove(AttributeWeights.class);
weight = weights.getWeight(attribute.getName());
}
if (!Double.isNaN(weight)) {
return new Benefit(weight, attribute);
} else {
return null;
}
}
public List<ParameterType> getParameterTypes() {
List<ParameterType> types = super.getParameterTypes();
// remove criterion selection
Iterator<ParameterType> i = types.iterator();
while (i.hasNext()) {
if (i.next().getKey().equals(PARAMETER_CRITERION))
i.remove();
}
return types;
}
}