Question

I’m basically trying to use an array, which is data that is read from a file, and then using that array calculate the mean and standard deviation from the data.

I just can’t seem to get the right number.

static public double[][] calcStats(String[][] x) throws IOException {
  double[][] array = new double[7][2];
  double total = 0, std_dev = 0, amount = 0;
  int row2 = 0;
  for (int row = 1; row < x.length; row++) {
    array[row2][0] = (total);
    array[row2][1] = Math.sqrt(amount);
    amount = 0;
    total = 0;
    if (row >= 2) {
      row2++;
    }
    for (int col = 1; col < x[row].length; col++) {
      total += Integer.parseInt(x[row][col]);
      if (col == 4) {
        total = (total / 4);
      }
    }
    for (int col = 1; col < x[row].length; col++) {
      std_dev = (Integer.parseInt(x[row][col])) - (total);
      std_dev = Math.pow(std_dev, 2);
      amount = +std_dev;
      std_dev = 0;
      if (col == 4) {
        amount = (amount / 27);
      }
    }
  }
  array[row2][0] = (total);
  return array;
}

Answer 1

Arrays in Java start at 0. You are starting your loops at 1. That means that you are missing the first element of each array.

As per Marko Topolnik’s suggestion, I should point out that I changed amount =+ std_dev; in your original code to amount += std_dev;. Now that I think about it, that was an invalid edit, since the original code was an additional problem (besides the loop limits). I rolled the edit back to Marco’s version.