Find common denominator for list entries Python

Question

I am calling a Python function several times and it returns a list with either one of the following:

1) single entry

2) multiple entry

3)blank list

For example:

a=['aaaaa']
b=['aaaaa', 'bbbbb', 'ccccc']
c=['aaaaa']
d=['ppppp', 'aaaaa']
e=['aaaaa', 'uuuuu']

Now, I want to find the common string in all the lists. I can do it as follows for TWO lists:

intercept_list=[val for val in a if val in b]

Is it possible to do it for multiple list in one go? Also supposing list "e" returned an empty list, I just want to ignore it.

Thank you

Answer 1

You can use intersection() :

>>> set(a).intersection(b, c, d, e)
set(['aaaaa'])

You can use list() to convert this back to a list:

result = list(set(a).intersection(b, c, d, e))

Answer 2

How about:

set.intersection(*(set(s) for s in list_of_lists if s))

For example:

>>> a=['aaaaa']
>>> b=['aaaaa', 'bbbbb', 'ccccc']
>>> c=['aaaaa']
>>> d=['ppppp', 'aaaaa']
>>> e=['aaaaa', 'uuuuu']
>>> f=[]
>>> list_of_lists = [a,b,c,d,e,f]
>>> set.intersection(*(set(s) for s in list_of_lists if s))
set(['aaaaa'])

Answer 3

A more generic implementation, counts the number of occurrence of the elements and verify if the count matches the list count

>>> def find_common(*args):
    from collections import Counter
    from itertools import takewhile, imap
    from operator import itemgetter
    count = sum(1 for e in args if e)
    args = chain.from_iterable(args)
    result =  map(itemgetter(0), 
                   takewhile(lambda e: e[-1] ==  count,
                             Counter(args).most_common()))
    return result

>>> find_common(a,b,c,d,e)
['aaaaa']
>>> f = []
>>> find_common(a,b,c,d,e, f)
['aaaaa']