[Numpy-discussion] np.histogramdd of empty data

Benjamin Root ben.root@ou....
Thu Mar 31 13:00:19 CDT 2011


On Thu, Mar 31, 2011 at 12:32 PM, Ralf Gommers
<ralf.gommers@googlemail.com>wrote:

> ---------- Forwarded message ----------
> From: Ralf Gommers <ralf.gommers@googlemail.com>
> Date: Thu, Mar 31, 2011 at 7:31 PM
> Subject: Re: [Numpy-discussion] np.histogramdd of empty data
> To: Nils Becker <n.becker@amolf.nl>
>
>
> On Thu, Mar 31, 2011 at 12:33 PM, Nils Becker <n.becker@amolf.nl> wrote:
> > Hi Ralf,
> >
> > I cloned numpy/master and played around a little.
> >
> > when giving the bins explicitely, now histogram2d and histogramdd work
> > as expected in all tests i tried.
> >
> >
> > However, some of the cases with missing bin specification appear
> > somewhat inconsistent.
> >
> > The first question is if creating arbitrary bins for empty data and
> > empty bin specification is better than raising an Exception:
> >
> > Specifically:
>
> Bins of size 0 should give a meaningful error, I was just fixing that
> as part of #1788 in
> https://github.com/rgommers/numpy/tree/ticket-1788-histogramdd
>
> > numpy.histogram2d([],[],bins=[0,0])
> >> (array([ 0.,  0.]), array([ 0.]), array([ 0.]))
>
> Now gives:
>    ValueError: Element at index 0 in `bins` should be a positive integer.
>
> > numpy.histogram([],bins=0)
> >> ValueError: zero-size array to minimum.reduce without identity
>
> Now gives:
>    ValueError: `bins` should be a positive integer.
>
>
> > so 1-d and 2-d behave not quite the same.
> >
> > also, these work (although with arbitrary bin edges):
> >
> > numpy.histogram2d([],[],bins=[1,1])
> >> (array([ 0.,  0.]), array([ 0.,  1.]), array([ 0.,  1.]))
> >
> > numpy.histogram2d([],[],bins=[0,1])
> >> (array([ 0.,  0.]), array([ 0.]), array([ 0.,  1.]))
> >
> > while this raises an error:
> >
> > numpy.histogram([],bins=1)
> >> ValueError: zero-size array to minimum.reduce without identity
>
> Now gives:
>    (array([0]), array([ 0.,  1.]))
>
>
Just for consistency's sake, maybe the same should be done for np.bincount()
and np.digitize() for empty data (but known bins)?  I don't know if your fix
to histogram does this or not, but the latest pull from numpy master doesn't
do this.

Thanks,
Ben Root
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