input: Write a function to calculate the average of the elements of a 2-dimensional array.
  
  def averageMatrix(matrix):
   sum = 0
   for row in matrix:
    for e in row:
     sum += e
  
   return sum / (len(matrix) * len(matrix[0]))
  
  a = [[3,2,6],
       [8,5,9],
       [4,7,1]]
  
  assert averageMatrix(a) == 4.77
  assert averageMatrix([[1,1],[1,1]]) == 1.0
  assert averageMatrix([]) == 0.0
  assert averageMatrix([[9,7,4],[2,8,6]]) == 6.0
  assert averageMatrix([[1],[5]]) == 3.0
output: def averageMatrix(matrix):
      if not matrix:
          return 0.0
      sum = 0
      count = 0
      for row in matrix:
          for e in row:
              sum += e
              count += 1
      return sum / count