[Numpy-discussion] simple indexing question
Robert Cimrman
cimrman3@ntc.zcu...
Wed Sep 23 08:59:24 CDT 2009
Neal Becker wrote:
> I have an array:
> In [12]: a
> Out[12]:
> array([[0, 1, 2, 3, 4],
> [5, 6, 7, 8, 9]])
>
> And a selection array:
> In [13]: b
> Out[13]: array([1, 1, 1, 1, 1])
>
> I want a 1-dimensional output, where the array b selects an element from
> each column of a, where if b[i]=0 select element from 0th row of a and if
> b[i]=k select element from kth row of a.
>
> Easy way to do this? (Not a[b], that gives 5x5 array output)
It might be stupid, but it works...
In [51]: a
Out[51]:
array([[0, 1, 2, 3, 4],
[5, 6, 7, 8, 9]])
In [52]: b = [0,1,0,1,0]
In [53]: a.T.flat[a.shape[0]*np.arange(a.shape[1])+b]
Out[53]: array([0, 6, 2, 8, 4])
cheers,
r.
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