How to intersect a lot of sets

Question

I have sets

{1, 2, 3, 4}
{2, 3, 4, 5}
{3, 4, 5, 6}
{4, 5, 6, 7}
{5, 6, 7, 8}

I need to intersect sets start from first. I mean that I should to intersect

{1, 2, 3, 4}
{2, 3, 4, 5}
{3, 4, 5, 6}

{2, 3, 4, 5}
{3, 4, 5, 6}
{4, 5, 6, 7}

and

{3, 4, 5, 6}
{4, 5, 6, 7}
{5, 6, 7, 8}

How can I do it in the loop? I know that I can use set1 & set2 & set3, but I don't know how can I do it with next set2 & set3 & set4 etc?

I don't understand what do you mean exactly? Are these sets inside a list? — AKS, May 26 '16 at 09:11

Daniel · Accepted Answer · 2016-05-26T09:59:34.550

2

First you need all your sets in a list, then iterate over your list in parallel with the zip-function:

sets = [
    {1, 2, 3, 4},
    {2, 3, 4, 5},
    {3, 4, 5, 6},
    {4, 5, 6, 7},
    {5, 6, 7, 8},
]

for s1, s2, s3 in zip(sets, sets[1:], sets[2:]):
    print(s1 & s2 & s3)

or more general:

AMOUNT_OF_SETS_TO_INTERSECT = 3
for sets_to_intersect in zip(*(sets[i:] for i in range(AMOUNT_OF_SETS_TO_INTERSECT))):
    print(set.intersection(*sets_to_intersect))

edited May 26 '16 at 09:59

answered May 26 '16 at 09:43

Daniel

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But if I have 60 sets, how can I do that? – NineWasps May 26 '16 at 09:56
60 sets to intersect? – Daniel May 26 '16 at 09:57
I have 60 sets and I want to intersect every 3 sets: `set1 & set2 & set3`, `set2 & set3 & set4`, `set3 & set4 & set5` , ... – NineWasps May 26 '16 at 10:02
So you have a list `sets` with 60 entries. What's the problem? – Daniel May 26 '16 at 10:04
I shoud use `sets[1:], sets[2:], sets[3:]` etc? Is any way to do it more readable? – NineWasps May 26 '16 at 10:10
You have to iterate your list three times in parallel, with different starting items; that's the most readable way. – Daniel May 26 '16 at 10:16

score 0 · Answer 2 · edited May 23 '17 at 12:08

If you are looking to find ways to do intersections of multiple sets, then this page has the answer, which basically tells you to use set.intersection() function

If you don't know how to put your sets inside a list and then traverse through it, it's a different question, which is basic Python.

In Python, you can put objects (including sets) inside a list and traverse through it as follows:

# Build the list of sets
set_list = []
for i in range(1, 6):
    set_list.append(set([i, i+1, i+2, i+3]))

# Now set_list contains the set (1,2,3,4), (2,3,4,5), ..., (5,6,7,8)

# Traverse and do set intersection
for i in range(len(set_list)-2):
    intersection = set.intersection(set_list[i], set_list[i+1], set_list[i+2])
    print(intersection)

# Will print:
# set([3, 4])
# set([4, 5])
# set([5, 6])

How to intersect a lot of sets

2 Answers2