python intersect of dict items

Question

ok another python question...

I have a dict:

aDict[1] = '3,4,5,6,7,8'
aDict[5] = '5,6,7,8,9,10,11,12'
aDict[n] = '5,6,77,88'

n could be any limit but the keys are not in sequence.

How do I extract the intersect of the csv'd items? So in this case the answer would be '5,6'.

Thanks

Answer 1

from functools import reduce # if Python 3

reduce(lambda x, y: x.intersection(y), (set(x.split(',')) for x in aDict.values()))

Answer 2

First of all, you need to convert these to real lists.

l1 = '3,4,5,6,7,8'.split(',')

Then you can use sets to do the intersection.

result = set(l1) & set(l2) & set(l3)

Answer 3

Python Sets are ideal for that task. Consider the following (pseudo code):

intersections = None
for value in aDict.values():
    temp = set([int(num) for num in value.split(",")])
    if intersections is None:
        intersections = temp
    else:
        intersections = intersections.intersection(temp)

print intersections

Answer 4

result = None
for csv_list in aDict.values():
    aList = csv_list.split(',')
    if result is None:
        result = set(aList)
    else:
        result = result & set(aList)
print result

Answer 5

Since set.intersection() accepts any number of sets, you can make do without any use of reduce():

set.intersection(*(set(v.split(",")) for v in aDict.values()))

Note that this version won't work for an empty aDict.

If you are using Python 3, and your dictionary values are bytes objects rather than strings, just split at b"," instead of ",".