python column split

Question

I have a python array in the format:

[[1,2,3],[4,5,6],[7,8,9]]

Is there a way for me to break it up into columns to give:

[[1,4,7],[2,5,8],[3,6,9]]

possible duplicate of [python list of lists transpose without zip(*m) thing](http://stackoverflow.com/questions/6473679/python-list-of-lists-transpose-without-zipm-thing) — senderle, Apr 12 '12 at 02:29
possible duplicate of [A Transpose/Unzip Function in Python](http://stackoverflow.com/questions/19339/a-transpose-unzip-function-in-python) — agf, Apr 12 '12 at 02:33
Is this really an array as specified by NumPy? Or an object of type `array` as created by the `array` module? Because what you've described looks instead like a `list`. — Karl Knechtel, Apr 12 '12 at 03:20

score 6 · Accepted Answer · answered Apr 12 '12 at 02:33

6

I think NumPy is good for this:

>>> import numpy as np
>>> my_list = [[1,2,3],[4,5,6],[7,8,9]]
>>> x = np.array(my_list)
>>> np.transpose(x).tolist()
[[1, 4, 7], [2, 5, 8], [3, 6, 9]]

answered Apr 12 '12 at 02:33

ely

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There is _no need_ for external libraries for something this simple. – agf Apr 12 '12 at 02:33
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That doesn't mean they aren't a good thing to use. There can be many good things to use, and knowing many of them is a good thing. – ely Apr 12 '12 at 02:34
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The OP mentioned array, so it makes sense to bring up numpy. – Akavall Apr 12 '12 at 02:42

avasal · Answer 2 · 2012-04-12T03:09:40.960

4

In [85]: [list(x) for x in zip(*[[1,2,3],[4,5,6],[7,8,9]])]
Out[85]: [[1, 4, 7], [2, 5, 8], [3, 6, 9]]

If you want list of tuples you can use:

In [86]: zip(*[[1,2,3],[4,5,6],[7,8,9]])
Out[86]: [(1, 4, 7), (2, 5, 8), (3, 6, 9)]

edited Apr 12 '12 at 03:09

answered Apr 12 '12 at 02:33

avasal

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The list comprehension is only necessary if you actually need the inner sequences to be lists. – agf Apr 12 '12 at 02:34
But in above case it seems to be lists, however if we don't put list(x) we will end up getting tuple which user doesn't want – avasal Apr 12 '12 at 02:39
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He shows them as lists, that doesn't mean he actually needs them to be lists. – agf Apr 12 '12 at 02:43
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You don't need list comprehension for 2nd case: zip(*[[1,2,3],[4,5,6],[7,8,9]]) – Akavall Apr 12 '12 at 02:59
Another way: `map(lambda *x: list(x), *[[1,2,3],[4,5,6],[7,8,9]])` – Karl Knechtel Apr 12 '12 at 03:21

python column split

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