/**
* 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.math.hadoop.similarity.cooccurrence.measures;
import org.apache.mahout.math.Vector;
import java.util.Iterator;
public class PearsonCorrelationSimilarity extends CosineSimilarity {
@Override
public Vector normalize(Vector vector) {
if (vector.getNumNondefaultElements() == 0) {
return vector;
}
// center non-zero elements
double average = vector.norm(1) / vector.getNumNondefaultElements();
Iterator<Vector.Element> nonZeroElements = vector.iterateNonZero();
while (nonZeroElements.hasNext()) {
Vector.Element nonZeroElement = nonZeroElements.next();
vector.setQuick(nonZeroElement.index(), nonZeroElement.get() - average);
}
return super.normalize(vector);
}
}