input: Write a python function to sort an array based on the absolute values of its elements.
  assert abs_sort([2, -5, -1, 3]) == [-1, 2, 3, -5]
  assert abs_sort([10, -3, 0, -2, 5]) == [0, -2, -3, 5, 10]
  assert abs_sort([-10, 3, -20, 15, 4]) == [3, 4, -10, 15, -20]
output: def abs_sort(arr):
      return sorted(arr, key=abs)