Sum of array in a different way

Let assume I have an MxN array and I should sum this array like in image as shown below;

Array sum

I should sum all x's , all y's , all z's and all g's. I need an approach. My_Brain.exe has stopped and I couldn't find any approach to solve this problem.

SumColumnZigZag(column) {
    Sum = 0
    for row = 0; row < rows; row++ {
        sum += array[row][column + (row % 2)*(1 - 2*(column % 2))]
    }
    return sum
}

% is the modulo operator