sum of columns in a 2 dimensional array

Question

static double [][] initialArray = {{7.432, 8.541, 23.398, 3.981}, {721.859, 6.9211, 29.7505, 53.6483}, {87.901, 455.72, 91.567, 57.988}};

public double[] columnSum(         


        

Answer 1

So close. The problem is that you are using array[i].length in your for loop. I changed it from array[i].length to array[0].length and your problem is gone. You need j there but you don't actually HAVE it yet.

You COULD do something like this although there isn't really any point if you know how you are going to get your array. Differently sized lists still would break the code for calculating sum though, you'd have to change that as well.

for (int i = 0, j = 0; i < initialArray[j].length; i++) {
  for (; j < initialArray.length; j++) {
    System.out.println(i + " " + j);
  }
  j = 0;
}

And here is your modified program.

public class Main {
  static double[][] initialArray = { { 7.432, 8.541, 23.398, 3.981 }, { 721.859, 6.9211, 29.7505, 53.6483 }, { 87.901, 455.72, 91.567, 57.988 } };

  public double[] columnSum(double[][] array) {
    int index = 0;
    double temp[] = new double[array[index].length];
    for (int i = 0; i < array[0].length; i++) {
      double sum = 0;
      for (int j = 0; j < array.length; j++) {
        sum += array[j][i];
      }
      temp[index] = sum;
      System.out.println("Index is: " + index + " Sum is: " + sum);
      index++;
    }
    return temp;
  }

  public static void main(String[] args) {
    new Main().columnSum(initialArray);
  }
}