The NumPy Fortran-ordering quiz
Travis Oliphant
oliphant.travis at ieee.org
Tue Oct 17 20:59:41 CDT 2006
Charles R Harris wrote:
>
>
> On 10/17/06, *Lisandro Dalcin* <dalcinl at gmail.com
> <mailto:dalcinl at gmail.com>> wrote:
>
> I was surprised by this
>
> In [14]: array([[1,2,3],[4,5,6]]).reshape((3,2),order='F')
> Out[14]:
> array([[1, 5],
> [4, 3],
> [2, 6]])
>
>
> This one still looks wrong.
>
> In [15]: array([1,2,3,4,5,6]).reshape((3,2),order='F')
> Out[15]:
> array([[1, 2],
> [3, 4],
> [5, 6]])
>
>
>
> This one is fixed,
>
> In [3]: array([[1,2,3,4,5,6]]).reshape((3,2),order='F')
> Out[3]:
> array([[1, 4],
> [2, 5],
> [3, 6]])
>
> I also don't understand why a copy is returned if 'F' just fiddles
> with the indices and strides; the underlying data should be the same,
> just the view changes. FWIW, I think both examples should be returning
> views.
You are right, it doesn't need to. My check is not general enough.
It can be challenging to come up with a general way to differentiate the
view-vs-copy situation and I struggled with it. In this case, it's the
fact that while self->nd > 1, the other dimensions are only of shape 1
and so don't really matter. If you could come up with some kind of
striding check that would distinguish the two cases, I would appreciate it.
-Travis
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