intersection of three sets in python?

python intersection set set-intersection
thephfactor picture thephfactor · Oct 8, 2012 · Viewed 8.6k times · Source

Currently I am stuck trying to find the intersection of three sets. Now these sets are really lists that I am converting into sets, and then trying to find the intersection of.

Here's what I have so far:

for list1 in masterlist:
    list1 = thingList1
for list2 in masterlist:
    list2 = thingList2
for list3 in masterlist:
    list3 = thingList3

d3 = [set(thingList1), set(thingList2), set(thingList3)] 
setmatches c = set.intersection(*map(set,d3)) 
print setmatches

and I'm getting

set([]) 
Script terminated.

I know there's a much simpler and better way to do this, but I can't find one...

EDIT

Okay, here's what I have now.

setList=()
setList2=()
setList3=()

for list1 in masterlist:
    setList=list1
    for list2 in masterlist:
        setList2=list2
        for list3 in masterlist:
            setList3=list3



setmatches=set(setList) & set(setList2) & set(setList3)
print setmatches

Still doesn't give me what I'm looking for: which is the one match I ensured was in each list. It's giving me what looks like an addition of all the sets.

Answer

mjgpy3 picture mjgpy3 · Oct 8, 2012

I think you are simply looking for:

set(thingList1) & set(thingList2) & set(thingList3)

The ampersand is intersection in Python (and some other languages as well).

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