/**************************************************
*   Author: Morrison
*   Date:  11 Nov 202020
**************************************************/
import java.util.ArrayList;
import java.util.OptionalDouble;
import java.util.Collections;

public class Stat
{
    
    public static void main(String[] args)
    {
        ArrayList<Double> al = new ArrayList<>();
        al.add(4.0);
        al.add(8.0);
        al.add(2.0);
        OptionalDouble result = mean(al);
        if(result.isPresent())
        {
            System.out.printf("The mean is %s\n", result.getAsDouble());
        }
        else
        {
            System.out.println("Your list was empty");
        }
        al.clear();
        for(int k = 1; k <=5;k++)
        {
            al.add(k*1.0);
        }
        result = median(al);
        if(result.isPresent())
        {
            System.out.printf("The median is %s\n", result.getAsDouble());
        }
        else
        {
            System.out.println("Your list was empty");
        }
        result = standardDeviation(al);
        if(result.isPresent())
        {
            System.out.printf("The standard deviation is %s\n", result.getAsDouble());
        }
        else
        {
            System.out.println("Your list was empty");
        }
        al.add(6.0);
       result = median(al);
        if(result.isPresent())
        {
            System.out.printf("The median is %s\n", result.getAsDouble());
        }
        else
        {
            System.out.println("Your list was empty");
        }
        result = standardDeviation(al);
        if(result.isPresent())
        {
            System.out.printf("The standard deviation is %s\n", result.getAsDouble());
        }
        else
        {
            System.out.println("Your list was empty");
        }
    }

    public static OptionalDouble mean(ArrayList<Double> x)
    {
        if(x.size() == 0)
        {
            return OptionalDouble.empty();
        }
        double total = 0;
        for(double d: x)
        {
            total += d;
        }
        return OptionalDouble.of(total/x.size());
    }
    public static OptionalDouble median(ArrayList<Double> x)
    {

        if(x.size() == 0)
        {
            return OptionalDouble.empty();
        }
        Collections.sort(x);
        int n = x.size();
        double out = n%2 == 1? x.get((n-1)/2):
            .5*(x.get(n/2 - 1) + x.get(n/2));
        return OptionalDouble.of(out);
    }
    public static OptionalDouble standardDeviation(ArrayList<Double> x)
    {
        if(x.size() == 0)
        {
            return OptionalDouble.empty();
        }
        double out = 0;
        double mu = mean(x).getAsDouble();
        for(double d: x)
        {
            out += (d - mu)*(d - mu);
        }
        out /= x.size();
        out = Math.sqrt(out);
        //sqrt((1/n)sum( x[k] - mean)**2)
        return OptionalDouble.of(out);
    }

}