How to compare a list of lists/sets in python?
So you want the difference between two lists of items.
first_list = [['Test.doc', '1a1a1a', 1111],
['Test2.doc', '2b2b2b', 2222],
['Test3.doc', '3c3c3c', 3333]]
secnd_list = [['Test.doc', '1a1a1a', 1111],
['Test2.doc', '2b2b2b', 2222],
['Test3.doc', '8p8p8p', 9999],
['Test4.doc', '4d4d4d', 4444]]
First I'd turn each list of lists into a list of tuples, so as tuples are hashable (lists are not) so you can convert your list of tuples into a set of tuples:
first_tuple_list = [tuple(lst) for lst in first_list]
secnd_tuple_list = [tuple(lst) for lst in secnd_list]
Then you can make sets:
first_set = set(first_tuple_list)
secnd_set = set(secnd_tuple_list)
EDIT (suggested by sdolan): You could have done the last two steps for each list in a one-liner:
first_set = set(map(tuple, first_list))
secnd_set = set(map(tuple, secnd_list))
Note: map
is a functional programming command that applies the function in the first argument (in this case the tuple
function) to each item in the second argument (which in our case is a list of lists).
and find the symmetric difference between the sets:
>>> first_set.symmetric_difference(secnd_set)
set([('Test3.doc', '3c3c3c', 3333),
('Test3.doc', '8p8p8p', 9999),
('Test4.doc', '4d4d4d', 4444)])
Note first_set ^ secnd_set
is equivalent to symmetric_difference
.
Also if you don't want to use sets (e.g., using python 2.2), its quite straightforward to do. E.g., with list comprehensions:
>>> [x for x in first_list if x not in secnd_list] + [x for x in secnd_list if x not in first_list]
[['Test3.doc', '3c3c3c', 3333],
['Test3.doc', '8p8p8p', 9999],
['Test4.doc', '4d4d4d', 4444]]
or with the functional filter
command and lambda
functions. (You have to test both ways and combine).
>>> filter(lambda x: x not in secnd_list, first_list) + filter(lambda x: x not in first_list, secnd_list)
[['Test3.doc', '3c3c3c', 3333],
['Test3.doc', '8p8p8p', 9999],
['Test4.doc', '4d4d4d', 4444]]
Not sure if there is a nice function for this, but the "manual" way to do it isn't difficult:
differences = []
for list in firstList:
if list not in secondList:
differences.append(list)