Create a 2D list out of 1D list

Question

I am a bit new to Python and I want to convert a 1D list to a 2D list, given the width and length of this matrix.

Say I have a list=[0,1,2,3] and I want to make a 2 by 2 matrix of this list.

How can I get matrix [[0,1],[2,3]] width=2, length=2 out of the list?

Probable duplicate - http://stackoverflow.com/q/3636344/1947535 — m.brindley, Feb 04 '13 at 06:48

score 42 · Accepted Answer · answered Feb 04 '13 at 06:51

42

Try something like that:

In [53]: l = [0,1,2,3]

In [54]: def to_matrix(l, n):
    ...:     return [l[i:i+n] for i in xrange(0, len(l), n)]

In [55]: to_matrix(l,2)
Out[55]: [[0, 1], [2, 3]]

answered Feb 04 '13 at 06:51

root

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Another example of why I love Python! Thanks @root! – propjk007 Jun 15 '16 at 15:51

score 11 · Answer 2 · answered Feb 04 '13 at 07:00

11

I think you should use numpy, which is purpose-built for working with matrices/arrays, rather than a list of lists. That would look like this:

>>> import numpy as np
>>> list_ = [0,1,2,3]
>>> a = np.array(list_).reshape(2,2)
>>> a
array([[0, 1],
       [2, 3]])
>>> a.shape
(2, 2)

Avoid calling a variable list as it shadows the built-in name.

answered Feb 04 '13 at 07:00

wim

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why is using numpy better than root's approach? – PhoonOne Feb 04 '13 at 07:06
4

It depends on what you need 2D structure for, but when you are working with matrices in almost any way numpy will be more efficient, convenient, and flexible. – wim Feb 04 '13 at 07:39
1

ValueError: cannot reshape array of size 1000000 into shape (2,2) – Tedo Vrbanec Oct 15 '18 at 07:46

Create a 2D list out of 1D list

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