/*
* 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.rules;
import com.rapidminer.example.Attribute;
import com.rapidminer.example.ExampleSet;
import com.rapidminer.example.set.SplittedExampleSet;
import com.rapidminer.operator.learner.tree.GreaterSplitCondition;
import com.rapidminer.operator.learner.tree.LessEqualsSplitCondition;
import com.rapidminer.operator.learner.tree.NominalSplitCondition;
import com.rapidminer.operator.learner.tree.SplitCondition;
/**
* Determines the best term for the given example set with respect to the criterion.
*
* @author Sebastian Land, Ingo Mierswa
* @version $Id: TermDetermination.java,v 1.8 2008/05/09 19:23:13 ingomierswa Exp $
*/
public class TermDetermination {
private Criterion criterion;
private NumericalSplitter splitter;
private double minValue;
public TermDetermination(Criterion criterion) {
this(criterion, Double.NEGATIVE_INFINITY);
}
public TermDetermination(Criterion criterion, double minValue) {
this.criterion = criterion;
splitter = new NumericalSplitter(criterion);
this.minValue = minValue;
}
public SplitCondition getBestTerm(ExampleSet exampleSet, String labelName) {
SplitCondition bestCondition = null;
double bestBenefit = Double.NEGATIVE_INFINITY;
double bestTotalWeight = 0;
for (Attribute attribute : exampleSet.getAttributes()) {
if (attribute.isNominal()) {
SplittedExampleSet splitted = SplittedExampleSet.splitByAttribute(exampleSet, attribute);
for (int i = 0; i < splitted.getNumberOfSubsets(); i++) {
SplittedExampleSet posSet = (SplittedExampleSet)splitted.clone();
posSet.selectSingleSubset(i);
SplittedExampleSet negSet = (SplittedExampleSet)splitted.clone();
negSet.selectAllSubsetsBut(i);
double[] benefits = this.criterion.getBenefit(posSet, negSet, labelName);
if ((benefits[0] > minValue) &&
(benefits[0] > 0) && (benefits[1] > 0) &&
((benefits[0] > bestBenefit) ||
((benefits[0] == bestBenefit) && (benefits[1] > bestTotalWeight)))) {
bestBenefit = benefits[0];
bestTotalWeight = benefits[1];
bestCondition = new NominalSplitCondition(attribute, posSet.iterator().next().getValueAsString(attribute));
}
}
} else {
Split bestSplit = splitter.getBestSplit(exampleSet, attribute, labelName);
double bestSplitValue = bestSplit.getSplitPoint();
if (!Double.isNaN(bestSplitValue)) {
double[] benefits = bestSplit.getBenefit();
if ((benefits[0] > minValue) &&
(benefits[0] > 0) && (benefits[1] > 0) &&
((benefits[0] > bestBenefit) ||
((benefits[0] == bestBenefit) && (benefits[1] > bestTotalWeight)))) {
bestBenefit = benefits[0];
bestTotalWeight = benefits[1];
if (bestSplit.getSplitType() == Split.LESS_SPLIT) {
bestCondition = new LessEqualsSplitCondition(attribute, bestSplitValue);
} else {
bestCondition = new GreaterSplitCondition(attribute, bestSplitValue);
}
}
}
}
}
return bestCondition;
}
}