[Numpy-discussion] matrix indexing question
Colin J. Williams
cjw@sympatico...
Sun Mar 25 18:16:13 CDT 2007
Alan G Isaac wrote:
> One thing keeps bugging me when I use numpy.matrix.
>
> All this is fine::
>
> >>> x=N.mat('1 1;1 0')
> >>> x
> matrix([[1, 1],
> [1, 0]])
> >>> x[1,:]
> matrix([[1, 0]])
>
> But it seems to me that I should be able
> to extract a matrix row as an array.
This can easily be done:
*** Python 2.5 (r25:51908, Sep 19 2006, 09:52:17) [MSC v.1310 32 bit
(Intel)] on win32. ***
>>> import numpy as _n
>>> A= _n.mat([[1, 2], [3, 4]])
>>> A[1]
matrix([[3, 4]])
>>> A[1].getA1()
array([3, 4])
An array and a matrix are different animals. Conversion from one to the
other should be spelled out.
As you have done below.
Colin W.
> So this ::
>
> >>> x[1]
> matrix([[1, 0]])
>
> feels wrong. (Similarly when iterating across rows.)
> Of course I realize that I can just ::
>
> >>> x.A[1]
> array([1, 0])
>
> but since the above keeps feeling wrong I felt I should
> raise this as a possible design issue, better discussed
> early than latter.
>
> Cheers,
> Alan Isaac
More information about the Numpy-discussion
mailing list