a list of tuples into two lists

Question

I have a list of tuples as follows: [(12,1),(123,4),(33,4)] and I want it to turn into [12,123,33] and [1,4,4] I was just wondering how I would go about this?

Cheers in advance

Answer 1

You could use zip():

zipped = [(12, 1), (123, 4), (33, 4)]
>>> b, c = zip(*zipped)
>>> b 
(12, 123, 33)
>>> c
(1, 4, 4)

Or you could achieve something similar using list comprehensions:

>>> b, c = [e[0] for e in zipped], [e[1] for e in zipped]
>>> b
[12, 123, 33]
>>> c
[1, 4, 4]

Difference being, one gives you a list of tuples (zip), the other a tuple of lists (the two list comprehensions).

In this case zip would probably be the more pythonic way and also faster.

Answer 2

This is a perfect use case for zip():

In [41]: l = [(12,1), (123,4), (33,4)]

In [42]: a, b = map(list, zip(*l))

In [43]: a
Out[43]: [12, 123, 33]

In [44]: b
Out[44]: [1, 4, 4]

If you don't mind a and b being tuples rather than lists, you can remove the map(list, ...) and just keep a, b = zip(*l).

Answer 3

This would be my go at it.

first_list = []
second_list = []

for tup in list_of_tuples:
    first_list.append(ls[0])
    second_list.append(ls[1])