org.apache.mahout.math.hadoop.similarity.cooccurrence.measures.PearsonCorrelationSimilarity Maven / Gradle / Ivy

/**
 * 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;

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.getNumNonZeroElements();
    for (Vector.Element e : vector.nonZeroes()) {
      e.set(e.get() - average);
    }
    return super.normalize(vector);
  }
}