input: Write a function to calculate the average of the elements in a 2-dimensional array. If the array is empty, return 0.0.
  def averageMatrix(matrix):
      if not matrix:
          return 0.0
      total = 0
      count = 0
      for row in matrix:
          for element in row:
              total += element
              count += 1
      return total / count
  
  assert averageMatrix([[3,2,6],[8,5,9],[4,7,1]]) == 5.0
  assert averageMatrix([]) == 0.0
  assert averageMatrix([[1,2,3],[4,5,6]]) == 3.5
  assert averageMatrix([[1],[2],[3]]) == 2.0
  assert averageMatrix([[1,2],[3,4]]) == 2.5
output: def averageMatrix(matrix):
      if not matrix:
          return 0.0
      total = 0
      count = 0
      for row in matrix:
          for element in row:
              total += element
              count += 1
      return total / count