/*
* RapidMiner
*
* Copyright (C) 2001-2007 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 General Public License as
* published by the Free Software Foundation; either version 2 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
* USA.
*/
package com.rapidminer.operator.olap.aggregation;
import com.rapidminer.example.Attribute;
/**
* Calculates the variance.
*
* @author Ingo Mierswa
* @version $Id: VarianceFunction.java,v 1.1 2007/05/27 22:02:41 ingomierswa Exp $
*
*/
public class VarianceFunction implements AggregationFunction {
public String getName() { return "variance"; }
public double calculate(double[] values) {
double sum = 0.0d;
for (double v : values)
sum += v;
double average = sum / values.length;
double varianceSum = 0.0d;
for (double v : values) {
double diff = average - v;
varianceSum += diff * diff;
}
return Math.sqrt(varianceSum);
}
public boolean supportsAttribute(Attribute attribute) {
return !attribute.isNominal();
}
}