input: Write a function to calculate the average of the elements in a 2-dimensional array. The function should return the average value. If the input array is empty, return 0.
  assert averageMatrix([[3, 2, 6], [8, 5, 9], [4, 7, 1]])==4.77
  assert averageMatrix([[1, 2], [3, 4]])==2.5
  assert averageMatrix([[1], [4], [7]])==4.0
  assert averageMatrix([[]])==0
  assert averageMatrix([])==0
output: def averageMatrix(matrix):
      if not matrix or not matrix[0]:
          return 0
      total = sum(sum(row) for row in matrix)
      count = sum(len(row) for row in matrix)
      return total / count