找到二维锯齿状数组的列的平均值

Question

I am trying to find the averages of columns of a jagged array but I get an error saying that arr[j].length when I'm dividing it by the sum, the j cannot find symbol. What can I do to fix this problem?

int maxC = arr[0].length;
for (int a = 1; a < arr.length; a++){
    if (arr[a].length > maxC){
        maxC = arr[a].length;
    }
}

for (int i = 0; i < maxC; i++){
    double sum = 0.0;
    for (int j = 0; j < arr.length; j++){
        if (i < arr[j].length){
            sum += arr[j][i];
        }
    }
    double avg = sum / arr[j].length;
    System.out.println("Average of col  " + (i + 1) +  "is: " + avg);  
}

Answer 1

Your variable j is declared in the inner for loop. Outside of that loop it does not exist. But the way I see it, you don't want to divide by the length of arr[j] , but by the number of numbers you added. That's arr.length minus the number of nested arrays that are too short.

The easiest way to fix this is to introduce a new variable that you increment inside your if statement, then divide by that variable instead of by arr[j].length .

Answer 2

It might be better to use row / col names instead of common i / j to improve code clarity. Also, a separate counter for the columns is needed to increment only when a column is present in a row to properly calculate the average:

for (int col = 0; col < maxC; col++) {
    double sum = 0.0;
    int colCount = 0;
    for (int row = 0; row < arr.length; row++) {
        if (col < arr[row].length) {
            sum += arr[row][col];
            colCount++;
        }
    }
    double avg = sum / colCount;
    System.out.println("Average of col #" + (col + 1) +  " is: " + avg);  
}