001/* 
002 * Copyright (c) 2012, Regents of the University of Colorado 
003 * All rights reserved.
004 * 
005 * Redistribution and use in source and binary forms, with or without
006 * modification, are permitted provided that the following conditions are met:
007 * 
008 * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 
009 * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 
010 * Neither the name of the University of Colorado at Boulder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. 
011 * 
012 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
013 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
014 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
015 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
016 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
017 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
018 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
019 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
020 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
021 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
022 * POSSIBILITY OF SUCH DAMAGE. 
023 */
024package org.cleartk.ml.feature.transform.extractor;
025
026import java.util.Map;
027
028/**
029 * 
030 * <br>
031 * Copyright (c) 2012, Regents of the University of Colorado <br>
032 * All rights reserved.
033 * 
034 * @author Lee Becker
035 */
036public class CosineSimilarity implements SimilarityFunction {
037
038  @Override
039  public double distance(Map<String, Double> vector1, Map<String, Double> vector2) {
040    return CosineSimilarity.dotProduct(vector1, vector2)
041        / (magnitude(vector1) * magnitude(vector2));
042  }
043
044  public static double dotProduct(Map<String, Double> vector1, Map<String, Double> vector2) {
045    double dot = 0.0;
046
047    if (vector1.size() > vector2.size()) {
048      Map<String, Double> tmp = vector2;
049      vector2 = vector1;
050      vector1 = tmp;
051    }
052
053    for (Map.Entry<String, Double> entry1 : vector1.entrySet()) {
054      if (vector2.containsKey(entry1.getKey())) {
055        dot += entry1.getValue() * vector2.get(entry1.getKey());
056      }
057    }
058
059    return dot;
060  }
061
062  public static double magnitude(Map<String, Double> vector) {
063    double mag = 0.0;
064    for (double v : vector.values()) {
065      mag += v * v;
066    }
067    return Math.sqrt(mag);
068  }
069
070}