python intersect of dict items

Question

Suppose I have a dict like:

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

The keys are arbitrary, and there could be any number of them. I want to consider every value in the dictionary.

I want to treat each string as comma-separated values, and find the intersection across the entire dictionary (the elements common to all dict values). So in this case the answer would be '5,6'. How can I do this?

score 4 · Accepted Answer · answered Oct 14 '11 at 09:29

4

from functools import reduce # if Python 3

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

answered Oct 14 '11 at 09:29

DrTyrsa

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ok now i'm getting error: TypeError: Type str doesn't support the buffer API. Any ideas? What if the is just 1 dict entry? What happens then? – khany Oct 14 '11 at 09:56
just as a guide the actual dict with 1 entry looks like:- {4: b'1,2,31,47,52,56'}. This is what is causing the error. – khany Oct 14 '11 at 10:01
@khany I haven't worked with Python 3, but I think [this](http://www.rmi.net/~lutz/strings30.html) will be helpful. BTW, if you are Python newbie and you don't have any special reasons for 3rd version, I highly recommend using Python 2, it is mainstream version today. – DrTyrsa Oct 14 '11 at 10:05
hmm I was using v3 to future proof my code but I am now looking into v2. – khany Oct 14 '11 at 10:18

score 3 · Answer 2 · answered Oct 14 '11 at 09:28

3

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)

answered Oct 14 '11 at 09:28

madjar

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incomplete answer as the dict has an indeterminable length – khany Oct 14 '11 at 09:31

Constantinius · Answer 3 · 2011-10-14T09:46:23.767

1

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

edited Oct 14 '11 at 09:46

answered Oct 14 '11 at 09:29

Constantinius

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AttributeError: 'dict' object has no attribute 'iteritems' – khany Oct 14 '11 at 09:36
@khany: What version do you use? It is a standard function since Python 2.2: http://docs.python.org/library/stdtypes.html#dict.iteritems – Constantinius Oct 14 '11 at 09:38
@khany It's because of Python 3, you should have mentioned that in your question. – DrTyrsa Oct 14 '11 at 09:38
@khany: depending on your version, you can also use `dict.items()`, this should work quite as good. – Constantinius Oct 14 '11 at 09:41
@Constantinius Do you really need `items()` here? You don't use `key` at all. – DrTyrsa Oct 14 '11 at 09:43
@DrTyrsa: correct. I'll change the answer. (Got mixed up, because my first attempt was to create a `dict` of `set`s, which was a stupid idea as I have found out). – Constantinius Oct 14 '11 at 09:46
@Constantinius yes it is Python 3.1 sorry I forgot to mention that. I hadn't marked your answer down though. – khany Oct 14 '11 at 09:55

score 0 · Answer 4 · answered Oct 14 '11 at 09:32

0

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

answered Oct 14 '11 at 09:32

Don

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Sven Marnach · Answer 5 · 2011-10-14T12:07:51.190

0

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 ",".

edited Oct 14 '11 at 12:07

answered Oct 14 '11 at 12:01

Sven Marnach

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python intersect of dict items

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