input: 
  from typing import List
  
  def averageMatrix(matrix: List[List[int]]) -> float:
      """ Calculate the average of all elements in a 2-dimensional array.
      >>> averageMatrix([[3,2,6], [8,5,9], [4,7,1]])
      5.111111111111111
      """
      sum = 0
      for row in matrix:
          for e in row:
              sum += e
  
      return sum / (len(matrix) * len(matrix[0]))
  
output:     sum = 0
      count = 0
      for row in matrix:
          for e in row:
              sum += e
              count += 1
  
      return sum / count