How to remove a sublist in nested list that are in another sublist?

Question

I had a list:

a = [[2,3,4],[2,3,4],[2,3],[1,5,4],[1,5]]

I want to get:

b = [[2,3,4],[1,5,4]]

[2,3,4] is duplicated and [2,3], [1,5] is completely contained by [2,3,4] , [1,5,4] , so I want to remove it

I use set(frozenset(x) for x in a) to remove duplicate but I got stuck by how to remove [2,3],[1,5] which are contained by another sublist in a

Answer 1

You can convert the sub-lists in a to sets and sort them by length in reverse order, so that you can iterate through them and add each set to the output only if it is not a subset of any of the existing sets in the output:

output = []
for candidate in sorted(map(set, a), key=len, reverse=True):
    if not any(candidate <= incumbent for incumbent in output):
        output.append(candidate)

list(map(list, output)) returns:

[[2, 3, 4], [1, 4, 5]]

Sets are unordered, however, so if the original item orders in the sub-lists are important, you can take advantage of the fact that dict keys are ordered since Python 3.7 and map the sub-lists to dict keys instead:

output = []
for candidate in sorted(map(dict.fromkeys, a), key=len, reverse=True):
    if not any(candidate.keys() <= incumbent.keys() for incumbent in output):
        output.append(candidate)

so that list(map(list, output)) returns:

[[2, 3, 4], [1, 5, 4]]

If you're using Python 3.6 or earlier versions, where the order of dict keys are not guaranteed, you can use collections.OrderedDict in place of dict.