source: src/main/java/negotiator/boaframework/opponentmodel/nash/StatisticsUtil.java

package negotiator.boaframework.opponentmodel.nash;

import java.util.ArrayList;


/**
 * This class contains methods that can be used for statistical measurements on lists.
 * 
 * @author Roland van der Linden
 *
 */
public class StatisticsUtil
{
        /**
         * This method adds the values in the list together and returns the sum.
         * @param list The list containing the values.
         * @return The sum of the values.
         */
        public static double getSum(ArrayList<Double> list)
        {
                if(list == null)
                        throw new IllegalArgumentException("The sum of a list that is null cannot be calculated.");
                
                double result = 0;
                
                for(Double d : list)
                        result += d;
                
                return result;
        }
        
        /**
         * This methods calculates the average value of the values in the list.
         * @param list The list containing the values.
         * @return The mean of the values.
         */
        public static double getMean(ArrayList<Double> list)
        {
                if(list == null)
                        throw new IllegalArgumentException("The mean of a list that is null cannot be calculated.");
                
                if(list.size() == 0)
                        return 0;
                else
                        return (getSum(list) / (double)list.size());
        }
        
        /**
         * This method calculates the variance of the values in the list.
         * @param list The list containing the values.
         * @return The variance of the values.
         */
        public static double getVariance(ArrayList<Double> list)
        {
                if(list == null)
                        throw new IllegalArgumentException("The variance of a list that is null cannot be calculated.");
                
                if(list.size() == 0)
                        return 0;
                else
                {
                        double mean = getMean(list);
                        double totalDifference = 0;
                        for(Double d : list)
                        {
                                double absdiff = Math.abs(d - mean);
                                double absdiff_squared = absdiff * absdiff;
                                totalDifference += absdiff_squared;
                        }
                
                        return (totalDifference / (double)list.size());
                }
        }
        
        /**
         * This method calculates the standard deviation of the values in the list.
         * @param list The list containing the values.
         * @return The standard deviation of the values.
         */
        public static double getStandardDeviation(ArrayList<Double> list)
        {
                if(list == null)
                        throw new IllegalArgumentException("The standardDeviation of a list that is null cannot be calculated.");
                
                if(list.size() == 0)
                        return 0;
                else
                {
                        double variance = getVariance(list);
                        return Math.sqrt(variance);
                }
        }
}