VarianceReductionSplitCriterion.java

package com.yahoo.labs.samoa.moa.classifiers.core.splitcriteria;

/*
 * #%L
 * SAMOA
 * %%
 * Copyright (C) 2013 - 2014 Yahoo! Inc.
 * %%
 * 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 com.yahoo.labs.samoa.moa.core.ObjectRepository;
import com.yahoo.labs.samoa.moa.options.AbstractOptionHandler;
import com.yahoo.labs.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
    }
    
}