input: Write a function to calculate the average of the elements in a 2-dimensional array. The function should take a matrix as input and return the average of all its elements. If the matrix is empty, the function should 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([[5]])==5
  assert averageMatrix([[]])==0
  assert averageMatrix([])==0
output: def averageMatrix(matrix):
      if not matrix or not matrix[0]:
          return 0
      total = 0
      count = 0
      for row in matrix:
          for elem in row:
              total += elem
              count += 1
      return total / count