/**
* Copyright (C) 2001-2017 by RapidMiner and the contributors
*
* Complete list of developers available at our web site:
*
* http://rapidminer.com
*
* This program is free software: you can redistribute it and/or modify it under the terms of the
* GNU Affero General Public License as published by the Free Software Foundation, either version 3
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
* even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License along with this program.
* If not, see http://www.gnu.org/licenses/.
*/
package com.rapidminer.operator.preprocessing.transformation.aggregation;
/**
* This is an {@link Aggregator} for the {@link VarianceAggregationFunction}
*
* @author Sebastian Land
*/
public class VarianceAggregator extends NumericalAggregator {
private double valueSum = 0d;
private double squaredValueSum = 0d;
private double totalWeightSum = 0d;
private double count = 0;
public VarianceAggregator(AggregationFunction function) {
super(function);
}
@Override
public void count(double value) {
valueSum += value;
squaredValueSum += value * value;
totalWeightSum++;
count++;
}
@Override
public void count(double value, double weight) {
valueSum += weight * value;
squaredValueSum += weight * value * value;
totalWeightSum += weight;
count++;
}
@Override
public double getValue() {
if (count > 0) {
return (squaredValueSum - valueSum * valueSum / totalWeightSum) / ((count - 1) / count * totalWeightSum);
} else {
return Double.NaN;
}
}
}