How to split the list on the pairwise elements?

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How do you split a list into evenly sized chunks in Python?

Let us have a list, there is always an even number of elements. We must break it down by pairing. Example: list['1','2','3','4'] need 1,2 and 3,4

score 3 · Answer 1 · answered Jun 15 '11 at 14:12

3

>>> L = [1, 2, 3, 4]
>>> pairs = zip(L[::2], L[1::2])
>>> print pairs
[(1, 2), (3, 4)]

Hope this helps

answered Jun 15 '11 at 14:12

inspectorG4dget

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score 1 · Answer 2 · edited May 23 '17 at 12:34

1

If you want two halfs of a list.

l = [1,2,3,4]
print l[:len(l)/2], l[len(l)/2:]
>>> [1, 2] [3, 4]

If you want split a list by pairs then your question is exact duplicate.

edited May 23 '17 at 12:34

Community

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answered Jun 15 '11 at 13:02

DrTyrsa

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and if have more elements [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] ? =)) – Denis Jun 15 '11 at 13:13

Artsiom Rudzenka · Answer 3 · 2011-06-15T13:52:01.773

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You can use something like this too:

lVals = xrange(1,101)
size = len(lVals)
output = ((lVals[i], lVals[i+1] if size > i+1 else None) for i in xrange(0, size, 2))

edited Jun 15 '11 at 13:52

answered Jun 15 '11 at 13:08

Artsiom Rudzenka

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I don't think this one works, try it out! – juanchopanza Jun 15 '11 at 13:19
@juanchopanza i have tried is several times and it works for me - if use 'res = list(output)' you will get a list of tuples for example: res[2] == (3,4) – Artsiom Rudzenka Jun 15 '11 at 13:31
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It gives (1,2),(2,3),(3,4) and so on, instead of (1,2),(3,4),(5,6) are required. You need output = ((lVals[i], lVals[i+1] if size > i+1 else None) for i in xrange(0,size,2)) – juanchopanza Jun 15 '11 at 13:34
@juanchopanza - yes, you right, my fault. Thanks for notifying me. – Artsiom Rudzenka Jun 15 '11 at 13:51

score 0 · Answer 4 · edited May 23 '17 at 12:26

Adapted from: How do you split a list into evenly sized chunks?

from itertools import izip_longest
data = range(6)
data_iters = [iter(data)] * 2
pairs = izip_longest(*data_iters)
[pair for pair in pairs]
>>> [(0, 1), (2, 3), (4, 5)]

The clever part is that the two elements of data_iters refer to the same object. Izip_longest alternately consumes from the two iterators passed as arguments, but since they're referring to the same object, it effectively pairs the elements in the iterator.

I take no credit for being clever here, upvote the comment I linked to if you liked my answer. :)

How to split the list on the pairwise elements?

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