The NumPy Fortran-ordering quiz

Travis Oliphant oliphant.travis at ieee.org
Tue Oct 17 21:15:13 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.

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.

-Travis


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