001    /*
002     * Copyright (C) 2008-2010 by Holger Arndt
003     *
004     * This file is part of the Universal Java Matrix Package (UJMP).
005     * See the NOTICE file distributed with this work for additional
006     * information regarding copyright ownership and licensing.
007     *
008     * UJMP is free software; you can redistribute it and/or modify
009     * it under the terms of the GNU Lesser General Public License as
010     * published by the Free Software Foundation; either version 2
011     * of the License, or (at your option) any later version.
012     *
013     * UJMP is distributed in the hope that it will be useful,
014     * but WITHOUT ANY WARRANTY; without even the implied warranty of
015     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
016     * GNU Lesser General Public License for more details.
017     *
018     * You should have received a copy of the GNU Lesser General Public
019     * License along with UJMP; if not, write to the
020     * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
021     * Boston, MA  02110-1301  USA
022     */
023    
024    package org.ujmp.core.util;
025    
026    /**
027     * This distance measure yields the <i>euclidian distance</i> between two
028     * samples of <code>double</code> values.
029     */
030    public class EuclidianDistance implements DistanceMeasure {
031    
032            /**
033             * Get the distance between two data samples.
034             * 
035             * @param sample1
036             *            the first sample of <code>double</code> values
037             * @param sample2
038             *            the second sample of <code>double</code> values
039             * @return the distance between <code>sample1</code> and
040             *         <code>sample2</code>
041             * @throws IllegalArgumentException
042             *             if the two samples contain different amounts of values
043             */
044            public double getDistance(double[] sample1, double[] sample2) throws IllegalArgumentException {
045    
046                    int n = sample1.length;
047                    if (n != sample2.length || n < 1)
048                            throw new IllegalArgumentException("Input arrays must have the same length.");
049    
050                    double sumOfSquares = 0;
051                    for (int i = 0; i < n; i++) {
052                            if (Double.isNaN(sample1[i]) || Double.isNaN(sample2[i]))
053                                    continue;
054    
055                            sumOfSquares += (sample1[i] - sample2[i]) * (sample1[i] - sample2[i]);
056                    }
057    
058                    return Math.sqrt(sumOfSquares);
059            }
060    }