How to create a list after every n terms

Question

I want to make [1,2,3,4,5,6,7,8] into [[1,2],[3,4],[5,6],[7,8]], but can't seem to figure out how.

Hey! This is a question for which there are many possible answers... Can you show what you tried so far? — rmeertens, Mar 13 '17 at 08:34
http://stackoverflow.com/questions/434287/what-is-the-most-pythonic-way-to-iterate-over-a-list-in-chunks — ewcz, Mar 13 '17 at 08:35
Naive and simple? `arr2 = [[arr[2*idx], arr[2*idx+1]] for idx in range(len(arr)/2)]` — BrechtDeMan, Mar 13 '17 at 08:39
FWIW, I like `zip(*[iter(yourList)] * chunksize)` and the `itertools.zip_longest` variation, although some people complain that they're a bit cryptic. — PM 2Ring, Mar 13 '17 at 08:39
@BrechtDeMan You should use floor division `//` for that instead of `/`. It won't make a difference in Python 2 (although it's semantically nicer to use the correct operator), but it will in Python 3, where `/` returns a `float`. — PM 2Ring, Mar 13 '17 at 08:49

score 0 · Answer 1 · answered Mar 13 '17 at 08:36

0

This will work:

>>> def to_matrix(l, n):
        return [l[i:i+n] for i in xrange(0, len(l), n)]

>>> l = [0,1,2,3]
>>> to_matrix(l,2)
>>> [[0, 1], [2, 3]]

Hope it helps

answered Mar 13 '17 at 08:36

Jeril

score 0 · Answer 2 · answered Mar 13 '17 at 08:38

0

A functional aproach:

l = [1,2,3,4,5,6,7,8]
map(list, zip(l[::2], l[1::2]))
[[1, 2], [3, 4], [5, 6], [7, 8]]

Also with iter:

it = iter(l)
zip(it, it)
[(1, 2), (3, 4), (5, 6), (7, 8)]

answered Mar 13 '17 at 08:38

Netwave

Note that in Python 3 both `map` and `zip` return iterators, not lists. – PM 2Ring Mar 13 '17 at 08:47

2 Answers2