Question

Using

def compare_lsts(list1,list2):
    first_set = set(list1)
    second_set=set(list2)
    results =[x for x in list1 if x in list2]
    print(results)

and running compare_lsts([1,2,3,4,5],[3,8,9,1,7]) gives the numbers contained in both sets, i.e. [1,3].

However making list 1 contain more than 1 list e.g. compare_lsts([[1,2,3,4,5],[5,8,2,9,12],[3,7,19,4,16]],[3,7,2,16,19]) gives [],[],[].

I have used for list in list1 followed by results for the loop. I clearly don’t know what I am doing.

Basically the question is: How does one compare items in one static list with as many lists as there are?

Answer 1

If you’re after elements from the first that are in all of the lists:

set(first).intersection(second, third) # fourth, fifth, etc...
>>> set([1, 2, 3]).intersection([2, 3, 4], [3, 4, 5])
set([3])

If you’re after elements from the first that are in any of the other lists:

>>> set([1, 2, 3]) & set([4]).union([5])
set([2])

So, then a simple func:

def in_all(fst, *rst):
    return set(fst).intersection(*rst)

def in_any(fst, *rst):
    it = iter(rst)
    return set(fst) & set(next(it, [])).union(*it)