How to find common elements in list of lists?

Question

I\'m trying to figure out how to compare an n number of lists to find the common elements. For example:

p=[ [1,2,3],
    [1,9,9],
      ..
      ..
    [1,2         


        

Answer 1

A simple solution (one-line) is:

set.intersection(*[set(list) for list in p])

Answer 2

p=[ [1,2,3],
    [1,9,9],
    [1,2,4]]

ans = [ele[0] for ele in zip(*p) if len(set(ele)) == 1]

Result:

>>> ans
[1]

Answer 3

You are looking for the set intersection of all the sublists, and the data type you should use for set operations is a set:

result = set(p[0])
for s in p[1:]:
    result.intersection_update(s)
print result

Answer 4

reduce(lambda x, y: x & y, (set(i) for i in p))

Answer 5

Why not just:

set.intersection(*map(set, p))

Result:

set([1])

Or like this:

ip = iter(p)
s = set(next(ip))
s.intersection(*ip)

Result:

set([1])

edit:

copied from console:

>>> p = [[1,2,3], [1,9,9], [1,2,4]]
>>> set.intersection(*map(set, p))
set([1])
>>> ip = iter(p)
>>> s = set(next(ip))
>>> s.intersection(*ip)
set([1])

Answer 6

You are looking for the set intersection of all the sublists, and the data type you should use for set operations is a set:

result = set(p[0])  
for s in p[1:]:
   result.intersection_update(s)
print result

However, there is a limitation of 10 lists in a list. Anything bigger causes 'result' list to be out of order. Assuming you've made 'result' into a list by list(result).

Make sure you result.sort() to ensure it's ordered if you depend on it to be that way.