如何获得二维数组的平均值

Question

I have a current method that is supposed to display the average of a 2D but it is outputting numbers that don't make sense For example; the average of 1.0,2.0,3.0,4.0,5.0,6.0 is 3.5 but my program is outputting the average as 10.5 for the numbers above.

Here is my method below

public static double getAverage(double[][] array1) {
        double total = 0; //Accumulator 
        int num = 0;

        for(int row = 0; row < array1.length; row++) 
        {
            for(int col =0; col < array1[row].length; col++) 
                total += array1 [row][col];
            num += 1;
        }
        return total / num;
}

Answer 1

A simple version would be

public static double getAverage(double[][] a) {
  return Arrays.stream(a)
          .flatMapToDouble(Arrays::stream)
          .average()
          .orElseThrow(() -> new IllegalArgumentException("no elements in the array"));
}

Your mistake is that you increment num in the row loop while you should do it inside the col loop.

A fun version would be

for (int row = 0; row < array1.length; row++)
  for (int col = 0; col < array1[row].length; total += array1[row][col++], num++);

Answer 2

You'r num variable is counting the numbers of rows and not the number of cells like it supposed to.

try instead of

 for(int col =0; col < array1[row].length; col++) 
            total += array1 [row][col];
        num += 1;

to do this:

for(int col =0; col < array1[row].length; col++) {
            total += array1 [row][col];
            num += 1;
}

[I have deleted a mistake that i wrote here]

Answer 3

Change num += 1; to

num += array1[row].length;

Answer 4

You're incrementing num inside the outer loop. You need to increment it in the inner loop for it to work as you expect:

public static double getAverage(double[][] array1) 
    {
        double total = 0; //Accumulator 
        int num = 0;

        for(int row = 0; row < array1.length; row++) 
        {
            for(int col =0; col < array1[row].length; col++) {
                 total += array1 [row][col];
                 num += 1;
            }
        }

        return total / num;
    }

A word of advice - just default to putting braces around your for loops. There's no point in risking bugs in order to save a couple of lines in your program.