python - Pythonic way of removing reversed duplicates in list

Question

I have a list of pairs:

[0, 1], [0, 4], [1, 0], [1, 4], [4, 0], [4, 1]

and I want to remove any duplicates where

[a,b] == [b,a]

So we end up with just

[0, 1], [0, 4], [1, 4]

I can do an inner & outer loop checking for the reverse pair and append to a list if that's not the case, but I'm sure there's a more Pythonic way of achieving the same results.

Answer 1

If you need to preserve the order of the elements in the list then, you can use a the sorted function and set comprehension with map like this:

lst = [0, 1], [0, 4], [1, 0], [1, 4], [4, 0], [4, 1]
data = {tuple(item) for item in map(sorted, lst)}
# {(0, 1), (0, 4), (1, 4)}

or simply without map like this:

data = {tuple(sorted(item)) for item in lst}

Another way is to use a frozenset as shown here however note that this only work if you have distinct elements in your list. Because like set, frozenset always contains unique values. So you will end up with unique value in your sublist(lose data) which may not be what you want.

To output a list, you can always use list(map(list, result)) where result is a set of tuple only in Python-3.0 or newer.