input: Write a function to calculate the sum of a 2D array using nested list comprehension.
  assert calculate_sum([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == 45
  assert calculate_sum([[0, 0, 0], [0, 0, 0], [0, 0, 0]]) == 0
  assert calculate_sum([[1, -1], [1, -1]]) == 0
output: def calculate_sum(arr):
      return sum([sum(row) for row in arr])