(Pierre GM: are you subscribed to this list? If so, sorry for cc-ing you.)
--- On Fri, 3/5/10, Friedrich Romstedt <friedrichromst...@gmail.com> wrote:
> From: Friedrich Romstedt <friedrichromst...@gmail.com>
> Subject: Re: [Matplotlib-users] Mysterious "ValueError: zero-size array..."
> To: "David Goldsmith" <d_l_goldsm...@yahoo.com>
> Date: Friday, March 5, 2010, 10:46 AM
> I can reproduce the error with:
>
> >>> argW = numpy.asarray([[0, 1, 2], [3, 4, 5],
> [6, 7, 8], [9, 10, 11]])
> >>> argW
> array([[ 0, 1, 2],
> [ 3, 4, 5],
> [ 6, 7, 8],
> [ 9, 10, 11]])
> >>> argW[0:1, 0:0]
> array([], shape=(1, 0), dtype=int32)
> >>> d1.axes.imshow(argW[0:1, 0:0])
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> File
> "D:\Programme\Programmierung\python-2.4.1\lib\site-packages\matplotlib\axes.py",
> line 5471, in imshow
> im.autoscale_None()
> File
> "D:\Programme\Programmierung\python-2.4.1\lib\site-packages\matplotlib\cm.py",
> line 148, in autoscale_None
> self.norm.autoscale_None(self._A)
> File
> "D:\Programme\Programmierung\python-2.4.1\lib\site-packages\matplotlib\colors.py",
> line 682, in autoscale_None
> if self.vmin is None: self.vmin =
> ma.minimum(A)
> File
> "D:\Programme\Programmierung\python-2.4.1\lib\site-packages\numpy\ma\core.py",
> line 3042, in __call__
> return self.reduce(a)
> File
> "D:\Programme\Programmierung\python-2.4.1\lib\site-packages\numpy\ma\core.py",
> line 3057, in reduce
> t = self.ufunc.reduce(target, **kargs)
> ValueError: zero-size array to ufunc.reduce without
> identity
>
> So it seems to me that you pass in an array with shape <
> 4 in at least
> one of the dimensions?
Thanks for your reply, Friedrich, and for creating the reproducing example!
I think it's a bug in numpy.ma._extrema_operations.reduce (at least Pierre GM
couldn't explain it away and instructed me to file a bug ticket on it over
there, which I did; w/ your permission, I'll add your code to that ticket?) -
at the very least, it should be able to handle zero-size arrays more robustly
(i.e., w/out raising an exception) IMO. Of course, that doesn't mean that once
it's been fixed, imshow (or cm, which is apparently what's really calling it)
won't encounter some other problem on account of the fix, but I guess we'll
have to cross that bridge when we come to it?
> NB: You lose at most 3 pixels at the border of your image
> when drawing
> it the method you proposed, because the int floor'ing will
> cause that.
I was afraid of that (fancy index math has never been one of my strong suits)
but ultimately I'm making ~5e3 x ~5e3 images (which is why I'm having to create
the images that way in the first place - I was getting a memory error trying to
imshow the whole full-resolution image w/ one call), so that loss is negligible
(but if you can show me how to avoid it, I'd be much appreciative).
> NB II: Something happened, you sent the last message four
> times?
Yeah, my apologies, I'm not sure why that happened; maybe was having
connectivity issues and wasn't sure if I'd sent it successfully? Anyway, sorry
'bout that. :-(
Thanks again!
DG
>
> Friedrich
>
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