weka.core.EditDistance.java Source code

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Here is the source code for weka.core.EditDistance.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/>.
 */

/*
 *    AbstractStringDistanceFunction.java
 *    Copyright (C) 2008 Bruno Woltzenlogel Paleo (http://www.logic.at/people/bruno/ ; http://bruno-wp.blogspot.com/)
 *
 */

package weka.core;

/**
 * Computes the Levenshtein edit distance between two strings.
 *
 * @author Bruno Woltzenlogel Paleo
 * @version $Revision$
 */
public class EditDistance extends AbstractStringDistanceFunction {

    public EditDistance() {
    }

    public EditDistance(Instances data) {
        super(data);
    }

    /**
     * Calculates the distance (Levenshtein Edit Distance) between two strings
     *
     * @param stringA the first string
     * @param stringB the second string
     * @return the distance between the two given strings
     */
    double stringDistance(String stringA, String stringB) {
        int lengthA = stringA.length();
        int lengthB = stringB.length();

        double[][] distanceMatrix = new double[lengthA + 1][lengthB + 1];

        for (int i = 0; i <= lengthA; i++) {
            distanceMatrix[i][0] = i;
        }

        for (int j = 1; j <= lengthB; j++) {
            distanceMatrix[0][j] = j;
        }

        for (int i = 1; i <= lengthA; i++) {
            for (int j = 1; j <= lengthB; j++) {
                if (stringA.charAt(i - 1) == stringB.charAt(j - 1)) {
                    distanceMatrix[i][j] = distanceMatrix[i - 1][j - 1];
                } else {
                    distanceMatrix[i][j] = 1 + Math.min(distanceMatrix[i - 1][j],
                            Math.min(distanceMatrix[i][j - 1], distanceMatrix[i - 1][j - 1]));
                }
            }
        }
        return distanceMatrix[lengthA][lengthB];
    }

    /**
     * Returns a string describing this object.
     * 
     * @return       a description of the evaluator suitable for
     *          displaying in the explorer/experimenter gui
     */
    public String globalInfo() {
        return "Implementing Levenshtein distance function.\n\n"
                + "One object defines not one distance but the data model in which "
                + "the distances between objects of that data model can be computed.\n\n"
                + "Attention: For efficiency reasons the use of consistency checks "
                + "(like are the data models of the two instances exactly the same), " + "is low.\n\n"
                + "For more information, see: http://en.wikipedia.org/wiki/Levenshtein_distance\n\n";
    }

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