Question

[JAVA] I need help creating a method to calculate the Standard Deviation of a 2D Array.

This is what I have so far:

public double calcStdDev() {
   int total = 0;

   for(int i = 0; i < arr.length; i++){
       total += arr[i][i];
   }

   double mean = total / arr.length;
   return mean;
}

The numbers I'm using at just 1,2,3,4,5,6 and the standard deviation is coming out wrong. Can I have help fixing my code?

Answer 1

package HomeworkLib1;
public class StdDev {
        public static void main(String[] args) {
                int[][] data = new int[3][3];
                int i, j;
                for(i=0; i<3; i++) {
                        for(j=0; j<3; j++) {
                                data[i][j] = (int)(Math.random()*10);                   //Randomly setting values for 2D array of size 3x3
                        }
                }
                int sum = 0;
                for(i=0; i<3; i++) {
                        for(j=0; j<3; j++) {
                                sum += data[i][j];
                        }
                }       
                for(i=0; i<3; i++) {
                        for(j=0; j<3; j++) {
                                System.out.print(data[i][j] + " ");
                        }
                        System.out.println();
                }
                System.out.println("Sum: "  + sum);
                double mean=0.0;                double variance=0.0;
                int size = data[0].length * data.length;
                mean = sum/size;
                for(i=0; i<3; i++) {
                        for(j=0; j<3; j++) {
                                variance += (mean - data[i][j])*(mean - data[i][j]);
                        }
                }
                variance /=size;
                double stdDev = Math.sqrt(variance);
                System.out.println("Mean: " + mean);
                System.out.println("Variance: " + variance);
                System.out.println("Standard Deviation: " + stdDev);
        }
}