[Numpy-discussion] how to assign to a "sub set" of an array

Sebastian Haase haase@msg.ucsf....
Wed Nov 14 11:13:57 CST 2007


On Nov 14, 2007 5:59 PM, Timothy Hochberg <tim.hochberg@ieee.org> wrote:
>
<snip>
>
>
> On Nov 14, 2007 9:08 AM, Sebastian Haase <haase@msg.ucsf.edu> wrote:
> > Hi,
> > First here is some test I ran, where I think the last command shows a bug:
> >
> > >>> a = N.arange(4); a.shape=2,2; a
> > [[0 1]
> >  [2 3]]
> > >>> aa = N.array((a,a,a)); aa
> > [[[0 1]
> >  [2 3]]
> >
> >  [[0 1]
> >  [2 3]]
> >
> >  [[0 1]
> >  [2 3]]]
> > >>> N.nonzero(a==0)
> > ([0], [0])
> > >>> aa[N.nonzero(a==0)] = 5,5; aa
> > [[[        5 544434034]
> >  [        2         3]]
> >
> >  [[        0         1]
> >  [        2         3]]
> >
> >  [[        0         1]
> >  [        2         3]]]
> >
> >
> > What happend here ?  The value 544434034 is different every time.....
>
> I'm not seeing that here on WinXP with numpy 1.0.4.dev3462 ; can you tell me
> what platform and version you are using?
>
>
>
>
> >
> > Background:
> > I have a gray-scale 2D image (in this examples it's a 2x2 pixel image
> named 'a')
> > I would like to show this image using grey-values EXCEPT I would like
> > to show 0-values as blue.
> > For use with pyOpenGL textures, I convert the image into an RGB image,
> > in the example called 'aa', with shape 3,2,2.
> >
> > This is where I'm getting lost, and I tried assigning "something"
> > (5,5) to aa "only at certain pixels"....
> > Maybe someone can teach what the proper indexing-constuct, that I
> > would need to do what I want.
> >
> > Did I find a bug ?
>
> It looks like a bug, although it's possible it's been fixed. Or maybe it's a
> new one and I need to update my version of numpy to see it...
>

I'm still on version 1.0,1 -- winXP. looks like it's fixed and I need
to upgrade ;-)

Thanks for checking,
-Sebastian


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