With this function you can get the height (number of entries) of a the first dimension of a 2D array. You supply the array to check and the output from the function tells you how many initial entries it contains. You can get the number of entries for the second dimension of the array using the function array_length_2d.
Argument Description array_index The index of the array to check.
for (var i = 0; i < array_height_2d(a);
for (var j = 0; j < array_length_2d(a, i); ++j;)
a[i, j] = -1;
The above code will loop through a 2D array and set each entry to -1.