[Numpy-discussion] indexing question

Ernest Adrogué eadrogue@gmx....
Mon Nov 22 14:01:21 CST 2010


22/11/10 @ 11:08 (-0800), thus spake Christopher Barker:
> On 11/21/10 11:37 AM, Ernest Adrogué wrote:
> >>so you want
> >>
> >>t[:,x,y]
> >
> >I tried that, but it's not the same:
> >
> >In [307]: t[[0,1],x,y]
> >Out[307]: array([1, 7])
> >
> >In [308]: t[:,x,y]
> >Out[308]:
> >array([[1, 3],
> >        [5, 7]])
> 
> what is your t? Here's my example, which I think matches what you asked for:
> 
> In [1]: import numpy as np
> 
> In [2]: a = np.arange(12)
> 
> In [3]: a.shape = (3,2,2)
> 
> In [4]: a
> Out[4]:
> array([[[ 0,  1],
>         [ 2,  3]],
> 
>        [[ 4,  5],
>         [ 6,  7]],
> 
>        [[ 8,  9],
>         [10, 11]]])
> 
> In [5]: a[:,1,0]
> Out[5]: array([ 2,  6, 10])

This works with scalar indices, but not with arrays.
The problem is that I don't want always the same element
from each subarray, but an arbitrary element, say the (1,0)
from the first, the (0,0) from the second, and so on,
so I have to use arrays.

-- 
Ernest


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