samoa-api/src/main/java/org/apache/samoa/moa/classifiers/core/splitcriteria/VarianceReductionSplitCriterion.java

/*
 * 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.samoa.moa.classifiers.core.splitcriteria;

import org.apache.samoa.moa.core.ObjectRepository;
import org.apache.samoa.moa.options.AbstractOptionHandler;
import org.apache.samoa.moa.tasks.TaskMonitor;

public class VarianceReductionSplitCriterion extends AbstractOptionHandler implements SplitCriterion {

  private static final long serialVersionUID = 1L;

  /*
   * @Override public double getMeritOfSplit(double[] preSplitDist, double[][]
   * postSplitDists) {
   * 
   * double N = preSplitDist[0]; double SDR = computeSD(preSplitDist);
   * 
   * // System.out.print("postSplitDists.length"+postSplitDists.length+"\n");
   * for(int i = 0; i < postSplitDists.length; i++) { double Ni =
   * postSplitDists[i][0]; SDR -= (Ni/N)*computeSD(postSplitDists[i]); }
   * 
   * return SDR; }
   */

  @Override
  public double getMeritOfSplit(double[] preSplitDist, double[][] postSplitDists) {
    double SDR = 0.0;
    double N = preSplitDist[0];
    int count = 0;

    for (int i1 = 0; i1 < postSplitDists.length; i1++) {
      double[] postSplitDist = postSplitDists[i1];
      double Ni = postSplitDist[0];
      if (Ni >= 5.0) {
        count = count + 1;
      }
    }

    if (count == postSplitDists.length) {
      SDR = computeSD(preSplitDist);
      for (int i = 0; i < postSplitDists.length; i++)
      {
        double Ni = postSplitDists[i][0];
        SDR -= (Ni / N) * computeSD(postSplitDists[i]);
      }
    }
    return SDR;
  }

  @Override
  public double getRangeOfMerit(double[] preSplitDist) {
    return 1;
  }

  public static double computeSD(double[] dist) {

    int N = (int) dist[0];
    double sum = dist[1];
    double sumSq = dist[2];
    // return Math.sqrt((sumSq - ((sum * sum)/N))/N);
    return (sumSq - ((sum * sum) / N)) / N;
  }

  @Override
  public void getDescription(StringBuilder sb, int indent) {
    // TODO Auto-generated method stub
  }

  @Override
  protected void prepareForUseImpl(TaskMonitor monitor,
      ObjectRepository repository) {
    // TODO Auto-generated method stub
  }

}