/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.mahout.common.distance;
import org.apache.hadoop.mapred.JobConf;
import org.apache.mahout.matrix.CardinalityException;
import org.apache.mahout.matrix.Vector;
import org.apache.mahout.common.parameters.Parameter;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
/**
* This class implements a cosine distance metric by dividing the dot product of two vectors by the product of their
* lengths
*/
public class CosineDistanceMeasure implements DistanceMeasure {
@Override
public void configure(JobConf job) {
// nothing to do
}
@Override
public Collection<Parameter<?>> getParameters() {
return Collections.emptyList();
}
@Override
public void createParameters(String prefix, JobConf jobConf) {
// nothing to do
}
public static double distance(double[] p1, double[] p2) {
double dotProduct = 0.0;
double lengthSquaredp1 = 0.0;
double lengthSquaredp2 = 0.0;
for (int i = 0; i < p1.length; i++) {
lengthSquaredp1 += p1[i] * p1[i];
lengthSquaredp2 += p2[i] * p2[i];
dotProduct += p1[i] * p2[i];
}
double denominator = Math.sqrt(lengthSquaredp1) * Math.sqrt(lengthSquaredp2);
// correct for floating-point rounding errors
if (denominator < dotProduct) {
denominator = dotProduct;
}
return 1.0 - (dotProduct / denominator);
}
@Override
public double distance(Vector v1, Vector v2) {
if (v1.size() != v2.size()) {
throw new CardinalityException();
}
double lengthSquaredv1 = 0.0;
Iterator<Vector.Element> iter = v1.iterateNonZero();
while (iter.hasNext()) {
Vector.Element elt = iter.next();
lengthSquaredv1 += elt.get() * elt.get();
}
iter = v2.iterateNonZero();
double lengthSquaredv2 = 0.0;
while (iter.hasNext()) {
Vector.Element elt = iter.next();
lengthSquaredv2 += elt.get() * elt.get();
}
double dotProduct = v1.dot(v2);
double denominator = Math.sqrt(lengthSquaredv1) * Math.sqrt(lengthSquaredv2);
// correct for floating-point rounding errors
if (denominator < dotProduct) {
denominator = dotProduct;
}
return 1.0 - (dotProduct / denominator);
}
@Override
public double distance(double centroidLengthSquare, Vector centroid, Vector v) {
return distance(centroid, v); // TODO
}
}