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

package org.apache.samoa.moa.classifiers.core.splitcriteria;

/*
 * #%L
 * SAMOA
 * %%
 * Copyright (C) 2014 - 2015 Apache Software Foundation
 * %%
 * Licensed 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.
 * #L%
 */

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
  }

}