The NumPy Fortran-ordering quiz

Charles R Harris charlesr.harris at gmail.com
Tue Oct 17 21:28:37 CDT 2006


On 10/17/06, Travis Oliphant <oliphant.travis at ieee.org> wrote:
>
> 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.
>
> Why does this look wrong.  What do you want it to be?  Perhaps you are
> thinking about the input array as C-order and the output array as
> Fortran order.   That's not what reshape does.   The order argument
> specifies how you think about both the input and output.
>
> Thus, reshape does the equivalent of a Fortran ravel to [1,4,2,5,3,6]
> and then a Fortran-order based fill of an empty (3,2) array:  giving you
> the result.


Why a Fortran ravel? I am thinking of it as preserving the memory layout,
just messing with how it is addressed.

Chuck
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