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

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.