/**
* 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 java.util.Iterator;
import org.apache.mahout.math.Vector;
/**
* This class implements a Euclidean distance metric by summing the square root of the squared differences
* between each coordinate, optionally adding weights.
*/
public class WeightedEuclideanDistanceMeasure extends WeightedDistanceMeasure {
@Override
public double distance(Vector p1, Vector p2) {
double result = 0;
Vector res = p2.minus(p1);
Vector theWeights = getWeights();
if (theWeights == null) {
Iterator<Vector.Element> iter = res.iterateNonZero();
while (iter.hasNext()) {
Vector.Element elt = iter.next();
result += elt.get() * elt.get();
}
} else {
Iterator<Vector.Element> iter = res.iterateNonZero();
while (iter.hasNext()) {
Vector.Element elt = iter.next();
result += elt.get() * elt.get() * theWeights.get(elt.index());
}
}
return Math.sqrt(result);
}
@Override
public double distance(double centroidLengthSquare, Vector centroid, Vector v) {
return distance(centroid, v); // TODO
}
}