>>> nubBy (\x y -> mod x 3 == mod y 3) [1,2,4,5,6] [1,2,6]
>>> nubBy (/=) [2, 7, 1, 8, 2, 8, 1, 8, 2, 8] [2,2,2]
>>> nubBy (>) [1, 2, 3, 2, 1, 5, 4, 5, 3, 2] [1,2,3,5,5]