[Numpy-discussion] another broadcast/fancy indexing question
Tue Jul 10 16:02:54 CDT 2007
On 7/10/07, Mark.Miller <firstname.lastname@example.org> wrote:
> Just ran across something that doesn't quite make sense to me at the
> Here's some code:
> >>> numpy.__version__
> >>> def f1(b,c):
> return b,c
> >>> b,c = numpy.fromfunction(f1,(5,5))
> >>> a=numpy.zeros((2,12,5,5),int)
> >>> a1=a
> >>> a1[:,b,c].shape
> (12, 5, 5)
> >>> a[0,:,b,c].shape
> (5, 5, 12) ###why does this not return (12,5,5)?
> So in a nutshell, it's not completely clear to me why these are
> returning arrays of different shapes. Can someone shed some light?
It's because you are using arrays as indices (aka Fancy-Indexing). When you
do this everything works differently. In this case, everything is being
broadcast to the same shape. As I understand it (and I try to use only the
simplest forms of fancy indexing), what you are doing is equivalent to:
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