New subject: np.histogramdd of empty data

31 Mar 2011

      ---------- Forwarded message ----------
From: Ralf Gommers 
Date: Thu, Mar 31, 2011 at 7:31 PM
Subject: Re: [Numpy-discussion] np.histogramdd of empty data
To: Nils Becker 

On Thu, Mar 31, 2011 at 12:33 PM, Nils Becker  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.]))
...
another thing with non-empty data:
numpy.histogram([1],bins=1)
...
(array([1]), array([ 0.5,  1.5]))
That is the correct answer.
...
numpy.histogram([1],bins=0)
...
(array([], dtype=int64), array([ 0.5]))
Now gives:
   ValueError: `bins` should be a positive integer.
...
while
numpy.histogram2d([1],[1],bins=A)
...
ValueError: zero-size array to minimum.reduce without identity
(here A==[0,0] or A==[0,1] but not A==[1,1] which gives a result)
Same sensible errors now, telling you bins elements shouldn't be 0.

Cheers,
Ralf

Re: [Numpy-discussion] np.histogramdd of empty data

Ralf Gommers

Benjamin Root

Ralf Gommers

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