/*
 *  RapidMiner
 *
 *  Copyright (C) 2001-2011 by Rapid-I and the contributors
 *
 *  Complete list of developers available at our web site:
 *
 *       http://rapid-i.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 StandardDeviationAggregator extends NumericalAggregator {

    private double valueSum = 0d;
    private double squaredValueSum = 0d;
    private double totalWeightSum = 0d;
    private double count = 0;

    public StandardDeviationAggregator(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) {
            double value =  (squaredValueSum - valueSum * valueSum / totalWeightSum) / ((count - 1) / count * totalWeightSum);
            if (value > 0d)
                return Math.sqrt(value);
            return 0d;
        } else
            return Double.NaN;
    }
}