[Numpy-discussion] how to cite 1Xn array as nX1 array?

Tony Yu tsyu80@gmail....
Fri Jan 27 08:36:46 CST 2012


On Fri, Jan 27, 2012 at 9:28 AM, Paul Anton Letnes <
paul.anton.letnes@gmail.com> wrote:

>
> On 27. jan. 2012, at 14:52, Chao YUE wrote:
>
> > Dear all,
> >
> > suppose I have a ndarray a:
> >
> > In [66]: a
> > Out[66]: array([0, 1, 2, 3, 4])
> >
> > how can use it as 5X1 array without doing a=a.reshape(5,1)?
>
> Several ways, this is one, although not much simpler.
> In [6]: a
> Out[6]: array([0, 1, 2, 3, 4])
>
> In [7]: a.shape = 5, 1
>
> In [8]: a
> Out[8]:
> array([[0],
>       [1],
>       [2],
>       [3],
>       [4]])
>
> Paul
>
>
I'm assuming your issue with that call to reshape is that you need to know
the dimensions beforehand. An alternative is to call:

>>> a.reshape(-1, 1)

The "-1" allows numpy to "infer" the length based on the given sizes.

Another alternative is:

>>> a[:, np.newaxis]

-Tony
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