/**
* 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.utils;
import org.apache.mahout.matrix.Vector;
/**
* This class implements a Euclidian 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);
if (weights == null) {
for (int i = 0; i < p1.cardinality(); i++) {
result += res.get(i) * res.get(i);
}
} else {
for (int i = 0; i < p1.cardinality(); i++) {
result += res.get(i) * res.get(i) * weights.get(i); // todo this is where the weights goes, right?
}
}
return Math.sqrt(result);
}
}