Re: [Numpy-discussion] addressing a submatrix

[Karol L. <kar...@kn...>]

On Wednesday 14 June 2006 11:14, Martin Wiechert wrote:
> Hi list,
>
> is there a concise way to address a subrectangle of a 2d array? So far I'm
> using
>
> A [I] [:, J]
>
> which is not pretty and more importantly only works for reading the
> subrectangle. Writing does *not* work. (Cf. session below.)
>
> Any help would be appreciated.
>
> Thanks,
> Martin

You can achieve this by using the "take" function twice, in this fashion:

>>> a =3D numpay.ones((10,10))
>>> for i in range(5):
=2E..  for j in range(5):
=2E..   a[i][j] =3D i+j
=2E..=20
>>> a
array([[0, 1, 2, 3, 4],
       [1, 2, 3, 4, 5],
       [2, 3, 4, 5, 6],
       [3, 4, 5, 6, 7],
       [4, 5, 6, 7, 8]])
>>> print a.take.__doc__
a.take(indices, axis=3DNone).  Selects the elements in indices from array a=
=20
along the given axis.
>>> a.take((1,2,3),axis=3D0)
array([[1, 2, 3, 4, 5],
       [2, 3, 4, 5, 6],
       [3, 4, 5, 6, 7]])
>>> a.take((1,2,3),axis=3D0).take((2,3),axis=3D1)
array([[3, 4],
       [4, 5],
       [5, 6]])

Cheers,
Karol

=2D-=20
written by Karol Langner
=B6ro cze 14 11:27:33 CEST 2006