weka.classifiers.evaluation.MarginCurve.java Source code

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Here is the source code for weka.classifiers.evaluation.MarginCurve.java

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/*
 *   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 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 General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 *    MarginCurve.java
 *    Copyright (C) 2002-2012 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.classifiers.evaluation;

import java.util.ArrayList;

import weka.core.Attribute;
import weka.core.DenseInstance;
import weka.core.Instance;
import weka.core.Instances;
import weka.core.RevisionHandler;
import weka.core.RevisionUtils;
import weka.core.Utils;

/**
 * Generates points illustrating the prediction margin. The margin is defined as
 * the difference between the probability predicted for the actual class and the
 * highest probability predicted for the other classes. One hypothesis as to the
 * good performance of boosting algorithms is that they increaes the margins on
 * the training data and this gives better performance on test data.
 * 
 * @author Len Trigg (len@reeltwo.com)
 * @version $Revision$
 */
public class MarginCurve implements RevisionHandler {

    /**
     * Calculates the cumulative margin distribution for the set of predictions,
     * returning the result as a set of Instances. The structure of these
     * Instances is as follows:
     * <p>
     * <ul>
     * <li><b>Margin</b> contains the margin value (which should be plotted as an
     * x-coordinate)
     * <li><b>Current</b> contains the count of instances with the current margin
     * (plot as y axis)
     * <li><b>Cumulative</b> contains the count of instances with margin less than
     * or equal to the current margin (plot as y axis)
     * </ul>
     * <p>
     * 
     * @return datapoints as a set of instances, null if no predictions have been
     *         made.
     */
    public Instances getCurve(ArrayList<Prediction> predictions) {

        if (predictions.size() == 0) {
            return null;
        }

        Instances insts = makeHeader();
        double[] margins = getMargins(predictions);
        int[] sorted = Utils.sort(margins);
        int binMargin = 0;
        int totalMargin = 0;
        insts.add(makeInstance(-1, binMargin, totalMargin));
        for (int element : sorted) {
            double current = margins[element];
            double weight = ((NominalPrediction) predictions.get(element)).weight();
            totalMargin += weight;
            binMargin += weight;
            if (true) {
                insts.add(makeInstance(current, binMargin, totalMargin));
                binMargin = 0;
            }
        }
        return insts;
    }

    /**
     * Pulls all the margin values out of a vector of NominalPredictions.
     * 
     * @param predictions a FastVector containing NominalPredictions
     * @return an array of margin values.
     */
    private double[] getMargins(ArrayList<Prediction> predictions) {

        // sort by predicted probability of the desired class.
        double[] margins = new double[predictions.size()];
        for (int i = 0; i < margins.length; i++) {
            NominalPrediction pred = (NominalPrediction) predictions.get(i);
            margins[i] = pred.margin();
        }
        return margins;
    }

    /**
     * Creates an Instances object with the attributes we will be calculating.
     * 
     * @return the Instances structure.
     */
    private Instances makeHeader() {

        ArrayList<Attribute> fv = new ArrayList<Attribute>();
        fv.add(new Attribute("Margin"));
        fv.add(new Attribute("Current"));
        fv.add(new Attribute("Cumulative"));
        return new Instances("MarginCurve", fv, 100);
    }

    /**
     * Creates an Instance object with the attributes calculated.
     * 
     * @param margin the margin for this data point.
     * @param current the number of instances with this margin.
     * @param cumulative the number of instances with margin less than or equal to
     *          this margin.
     * @return the Instance object.
     */
    private Instance makeInstance(double margin, int current, int cumulative) {

        int count = 0;
        double[] vals = new double[3];
        vals[count++] = margin;
        vals[count++] = current;
        vals[count++] = cumulative;
        return new DenseInstance(1.0, vals);
    }

    /**
     * Returns the revision string.
     * 
     * @return the revision
     */
    @Override
    public String getRevision() {
        return RevisionUtils.extract("$Revision$");
    }

    /**
     * Tests the MarginCurve generation from the command line. The classifier is
     * currently hardcoded. Pipe in an arff file.
     * 
     * @param args currently ignored
     */
    public static void main(String[] args) {

        try {
            Utils.SMALL = 0;
            Instances inst = new Instances(new java.io.InputStreamReader(System.in));
            inst.setClassIndex(inst.numAttributes() - 1);
            MarginCurve tc = new MarginCurve();
            EvaluationUtils eu = new EvaluationUtils();
            weka.classifiers.meta.LogitBoost classifier = new weka.classifiers.meta.LogitBoost();
            classifier.setNumIterations(20);
            ArrayList<Prediction> predictions = eu.getTrainTestPredictions(classifier, inst, inst);
            Instances result = tc.getCurve(predictions);
            System.out.println(result);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}