[Numpy-discussion] array indexing problem

Bill Baxter wbaxter at gmail.com
Tue Aug 29 19:02:24 CDT 2006


That's just the way it works in numpy.  Slices return arrays of lower rank.
If you want arrays that behave like they do in linear algebra you can
use 'matrix' instead.  Check out the Numpy for Matlab users page for
more info on array vs. matrix.
http://www.scipy.org/NumPy_for_Matlab_Users

--bb

On 8/30/06, Rahul Kanwar <rkanwar at geol.sc.edu> wrote:
> Hello,
>
>    I am trying to extract a column from a 2D array here is what is have
> done:
>
> --------------------------------------------
> In [3]: a = array([[1,2,3],[1,2,3]])
>
> In [4]: a
> Out[4]:
> array([[1, 2, 3],
>        [1, 2, 3]])
>
> In [5]: a[:, 1]
> Out[5]: array([2, 2])
>
> In [6]: a[:, 1:2]
> Out[6]:
> array([[2],
>        [2]])
> --------------------------------------------
>
> when i use a[:, 1] i get a 1x2 array where as when i use a[:, 1:2] i get
> a 2x1 array. The intuitive behavior of a[:, 1] should be a 2x1 array. Am
> i doing something wrong here or is there some reason for this behavior ?
>
> regards,
> Rahul
>
>
>
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