How to get the Standard deviation of this array

Question

Ok so i have a code set out to get the mean of an array that has upto 50 elements, i want to also find the standard deviation of those elements and show it right under where it would display the mean, my code so far is

import java.util.Scanner;

public class caArray
{
public static void main(String args[])
{
    Scanner input = new Scanner(System.in);
    System.out.println("How many numbers you want to calculate average upto 50 : ");

    int n = input.nextInt();
    int[] array = new int[50];
    int sum = 0;


    for (int m = 0; m < n; m++)
    {
        System.out.print("Number " + m + " : ");
        array[m] = input.nextInt();
    }


    for (int m = 0; m < n; m++)
    {
        sum = array[m] + sum;
    }


    {
        System.out.println("Total value of Numbers = " + sum);
    }


    {
        double avg;
        avg = sum / array.length;
        System.out.println("Average of Numbers = " + avg);  //calculate average value
    }
}
}

i need to add into this to get the standard deviation in the one program

EDIT** I cannot use the functions as i actully have to use the standard deviation fourmula withing the program itself

Answer 1

you can write it in 3 Methods

private double standardDeviation(double[] input) {
    return Math.sqrt(variance(input));
}

private double variance(double[] input) {
    double expectedVal = expectedValue(input);
    double variance = 0;
    for(int i = 0;i<input.length;++i) {
        double buffer = input[i] - expectedVal;
        variance += buffer * buffer;
    }
    return variance;
}

private double expectedValue(double[] input) {
    double sum = 0;
    for(int i = 0;i<input.length;++i) {
        sum += input[i];
    }
    return sum/input.length;
}

hope it works, i am not quite shure about it, if i used the formulas the right way.

But basicly you have this 3 mathematical formulas in your calculation

Answer 2

If you don't have to write it yourself, check out Apache Commons Math . The stats documentation references how to derive standard deviations .

As you have to write it yourself, perhaps checking out the source code for DescriptiveStatistics would be instructive (look for the function getStandardDeviation() )