On 10/17/06, Travis Oliphant <[EMAIL PROTECTED]> wrote:
I suppose the problem is mostly in discontiguous arrays. Hmmm..., this isn't too different that reshaping the transpose.
a.reshape((m,n),order='F' ~ a.reshape((n,m)).T.reshape(m,n)
for instance:
In [26]: a
Out[26]:
array([[1, 2, 3],
[4, 5, 6]])
In [27]: a.reshape((3,2)).T.reshape((2,3))
Out[27]:
array([[1, 3, 5],
[2, 4, 6]])
In [28]: a.reshape((2,3), order='F')
Out[28]:
array([[1, 2, 3],
[4, 5, 6]])
Where I actually think the second reshape is correct and the third incorrect. This has the advantage that *all* the steps return views.
Chuck
Charles R Harris wrote:
>
>
> On 10/17/06, *Lisandro Dalcin* <[EMAIL PROTECTED]
> <mailto:[EMAIL PROTECTED]>> 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.
I suppose the problem is mostly in discontiguous arrays. Hmmm..., this isn't too different that reshaping the transpose.
a.reshape((m,n),order='F' ~ a.reshape((n,m)).T.reshape(m,n)
for instance:
In [26]: a
Out[26]:
array([[1, 2, 3],
[4, 5, 6]])
In [27]: a.reshape((3,2)).T.reshape((2,3))
Out[27]:
array([[1, 3, 5],
[2, 4, 6]])
In [28]: a.reshape((2,3), order='F')
Out[28]:
array([[1, 2, 3],
[4, 5, 6]])
Where I actually think the second reshape is correct and the third incorrect. This has the advantage that *all* the steps return views.
Chuck
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