[[a,b], [b,a], [c,d], [d,c]] etc.2nd pair deletion

Question

If I have a list such as

[[a,b], [b,a], [c,d], [d,c]]

But with letter pair lists not adjacent, how do I iterate through the list and end up with only one of the letter pairs?

Answer 1

If you don't care about order then the easiest way is to use sets and frozensets:

lst = [[a,b], [b,a], [c,d], [d,c]] 
result =  [list(x) for x in {frozenset(t) for t in lst}]

# result output: [[a,b], [c,d]]

Since frozenset([a,b]) == frozenset([b,a]), the set comprehension {frozenset(t) for t in lst} will include each pair only once. The outer list comprehension converts back the set of frozensets to a list of lists.