DecisionStump.java

/*
 *    DecisionStump.java
 *    Copyright (C) 2007 University of Waikato, Hamilton, New Zealand
 *    @author Richard Kirkby (rkirkby@cs.waikato.ac.nz)
 *
 *    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.
 */
package tr.gov.ulakbim.jDenetX.classifiers;

import tr.gov.ulakbim.jDenetX.classifiers.attributes.AttributeClassObserver;
import tr.gov.ulakbim.jDenetX.classifiers.attributes.AttributeSplitSuggestion;
import tr.gov.ulakbim.jDenetX.classifiers.attributes.GaussianNumericAttributeClassObserver;
import tr.gov.ulakbim.jDenetX.classifiers.attributes.NominalAttributeClassObserver;
import tr.gov.ulakbim.jDenetX.classifiers.splits.SplitCriterion;
import tr.gov.ulakbim.jDenetX.core.AutoExpandVector;
import tr.gov.ulakbim.jDenetX.core.DoubleVector;
import tr.gov.ulakbim.jDenetX.core.Measurement;
import tr.gov.ulakbim.jDenetX.options.ClassOption;
import tr.gov.ulakbim.jDenetX.options.FlagOption;
import tr.gov.ulakbim.jDenetX.options.IntOption;
import weka.core.Instance;

public class DecisionStump extends AbstractClassifier {

    private static final long serialVersionUID = 1L;

    public IntOption gracePeriodOption = new IntOption("gracePeriod", 'g',
            "The number of instances to observe between model changes.", 1000,
            0, Integer.MAX_VALUE);

    public FlagOption binarySplitsOption = new FlagOption("binarySplits", 'b',
            "Only allow binary splits.");

    public ClassOption splitCriterionOption = new ClassOption("splitCriterion",
            'c', "Split criterion to use.", SplitCriterion.class,
            "InfoGainSplitCriterion");

    protected AttributeSplitSuggestion bestSplit;

    protected DoubleVector observedClassDistribution;

    protected AutoExpandVector<AttributeClassObserver> attributeObservers;

    protected double weightSeenAtLastSplit;

    @Override
    public void resetLearningImpl() {
        this.bestSplit = null;
        this.observedClassDistribution = new DoubleVector();
        this.attributeObservers = new AutoExpandVector<AttributeClassObserver>();
        this.weightSeenAtLastSplit = 0.0;
    }

    @Override
    protected Measurement[] getModelMeasurementsImpl() {
        Measurement[] measurement = null;
        return measurement;
    }

    @Override
    public void getModelDescription(StringBuilder out, int indent) {
        // TODO Auto-generated method stub

    }

    @Override
    public void trainOnInstanceImpl(Instance inst) {
        this.observedClassDistribution.addToValue((int) inst.classValue(), inst
                .weight());
        for (int i = 0; i < inst.numAttributes() - 1; i++) {
            int instAttIndex = modelAttIndexToInstanceAttIndex(i, inst);
            AttributeClassObserver obs = this.attributeObservers.get(i);
            if (obs == null) {
                obs = inst.attribute(instAttIndex).isNominal() ? newNominalClassObserver()
                        : newNumericClassObserver();
                this.attributeObservers.set(i, obs);
            }
            obs.observeAttributeClass(inst.value(instAttIndex), (int) inst
                    .classValue(), inst.weight());
        }
        if (this.trainingWeightSeenByModel - this.weightSeenAtLastSplit >= this.gracePeriodOption
                .getValue()) {
            this.bestSplit = findBestSplit((SplitCriterion) getPreparedClassOption(this.splitCriterionOption));
            this.weightSeenAtLastSplit = this.trainingWeightSeenByModel;
        }
    }

    public double[] getVotesForInstance(Instance inst) {
        if (this.bestSplit != null) {
            int branch = this.bestSplit.splitTest.branchForInstance(inst);
            if (branch >= 0) {
                return this.bestSplit
                        .resultingClassDistributionFromSplit(branch);
            }
        }
        return this.observedClassDistribution.getArrayCopy();
    }

    public boolean isRandomizable() {
        return false;
    }

    protected AttributeClassObserver newNominalClassObserver() {
        return new NominalAttributeClassObserver();
    }

    protected AttributeClassObserver newNumericClassObserver() {
        return new GaussianNumericAttributeClassObserver();
    }

    protected AttributeSplitSuggestion findBestSplit(SplitCriterion criterion) {
        AttributeSplitSuggestion bestFound = null;
        double bestMerit = Double.NEGATIVE_INFINITY;
        double[] preSplitDist = this.observedClassDistribution.getArrayCopy();
        for (int i = 0; i < this.attributeObservers.size(); i++) {
            AttributeClassObserver obs = this.attributeObservers.get(i);
            if (obs != null) {
                AttributeSplitSuggestion suggestion = obs
                        .getBestEvaluatedSplitSuggestion(criterion,
                                preSplitDist, i, this.binarySplitsOption
                                .isSet());
                if (suggestion.merit > bestMerit) {
                    bestMerit = suggestion.merit;
                    bestFound = suggestion;
                }
            }
        }
        return bestFound;
    }

}