input: Write a function to calculate the average of the elements of a 2-dimensional array. If the matrix is empty, return 0.
  def averageMatrix(matrix):
   if not matrix:
    return 0
   total_sum = 0
   num_elements = 0
   for row in matrix:
    for element in row:
     total_sum += element
     num_elements += 1
   return total_sum / num_elements
  
  assert averageMatrix([[3, 2, 6], [8, 5, 9], [4, 7, 1]]) == 5.333333333333333
  assert averageMatrix([[1, 2], [3, 4]]) == 2.5
  assert averageMatrix([[10]]) == 10
  assert averageMatrix([]) == 0
  assert averageMatrix([[0, 0], [0, 0]]) == 0
output: def averageMatrix(matrix):
   if not matrix:
    return 0
   total_sum = 0
   num_elements = 0
   for row in matrix:
    for element in row:
     total_sum += element
     num_elements += 1
   return total_sum / num_elements