input: Write a function to calculate the average of all elements in a 2-dimensional array. The function should return the average as a floating-point number. If the given array is empty, the function should return 0.
  
  assert averageMatrix([[3, 2, 6], [8, 5, 9], [4, 7, 1]])==5.0
  assert averageMatrix([[1, 2], [3, 4]])==2.5
  assert averageMatrix([[0, 0], [0, 0]])==0.0
  assert averageMatrix([[]])==0.0
  assert averageMatrix([])==0.0
output: def averageMatrix(matrix):
      if not matrix or not matrix[0]:
          return 0.0
      total = 0
      count = 0
      for row in matrix:
          for element in row:
              total += element
              count += 1
      return total / count if count != 0 else 0.0