Splitting a list into two seperate lists, by every other item in python

Question

Hello I have a quick question I cant seem to solve.

I have a list:

a = [item1, item2, item3, item4, item5, item6]

And I want to split this list into two seperate ones by everything other item such that:

b = [item1, item3, item5]
c = [item2, item4, item6]

possible duplicate of [Python program to split a list into two lists with alternating elements](http://stackoverflow.com/questions/1442782/python-program-to-split-a-list-into-two-lists-with-alternating-elements) — devnull, Mar 04 '14 at 03:19

score 6 · Answer 1 · answered Mar 04 '14 at 03:11

6

Use slicing, specifying a step:

b,c = a[::2], a[1::2]

answered Mar 04 '14 at 03:11

roippi

The result you want is then zip(b, c). – holdenweb Mar 04 '14 at 04:14
1

Sorry - I was answering another question :-). Your solution is great - upvoted. – holdenweb Mar 04 '14 at 04:25

score 0 · Answer 2 · answered Mar 04 '14 at 03:11

0

Using filter is one option:

a = [item1, item2, item3, item4, item5, item6]
b = filter(lambda x: a.index(x) % 2 == 0, a)
c = filter(lambda x: a.index(x) % 2 != 0, a)

EDIT: This would require for the elements to be unique and is inefficient.

answered Mar 04 '14 at 03:11

shaktimaan

This doesn't work if the list contains equal items, and even when all list elements are unique, it runs in quadratic time instead of linear. – user2357112 Mar 04 '14 at 03:12

2 Answers2