[Numpy-discussion] np.bincount raises MemoryError when given an empty array

Charles R Harris charlesr.harris@gmail....
Tue Feb 2 01:01:50 CST 2010


On Mon, Feb 1, 2010 at 10:57 PM, <josef.pktd@gmail.com> wrote:

> On Tue, Feb 2, 2010 at 12:31 AM, Charles R Harris
> <charlesr.harris@gmail.com> wrote:
> >
> >
> > On Mon, Feb 1, 2010 at 10:02 PM, <josef.pktd@gmail.com> wrote:
> >>
> >> On Mon, Feb 1, 2010 at 11:45 PM, Charles R Harris
> >> <charlesr.harris@gmail.com> wrote:
> >> >
> >> >
> >> > On Mon, Feb 1, 2010 at 9:36 PM, David Cournapeau <cournape@gmail.com>
> >> > wrote:
> >> >>
> >> >> On Tue, Feb 2, 2010 at 1:05 PM,  <josef.pktd@gmail.com> wrote:
> >> >>
> >> >> > I think this could be considered as a correct answer, the count of
> >> >> > any
> >> >> > integer is zero.
> >> >>
> >> >> Maybe, but this shape is random - it would be different in different
> >> >> conditions, as the length of the returned array is just some random
> >> >> memory location.
> >> >>
> >> >> >
> >> >> > Returning an array with one zero, or the empty array or raising an
> >> >> > exception? I don't see much of a pattern
> >> >>
> >> >> Since there is no obvious solution, the only rationale for not
> raising
> >> >> an exception  I could see is to accommodate often-encountered special
> >> >> cases. I find returning [0] more confusing than returning empty
> >> >> arrays, though - maybe there is a usecase I don't know about.
> >> >>
> >> >
> >> > In this case I would expect an empty input to be a programming error
> and
> >> > raising an error to be the right thing.
> >>
> >> Not necessarily, if you run the bincount over groups in a dataset and
> >> your not sure if every group is actually observed. The main question,
> >> is whether the user needs or wants to check for empty groups before or
> >> after the loop over bincount.
> >>
> >
> > How would they know which bin to check? This seems like an unlikely way
> to
> > check for an empty input.
>
> # grade (e.g. SAT) distribution by school and race
> for s in schools:
>    for r in race:
>      print s, r, np.bincount(allstudentgrades[(sch==s)*(ra==r)])
>
> allwhite schools and allblack schools raise an exception.
>
> I just made up the story, my first attempt was: all sectors, all
> firmsize groups, bincount something, will have empty cells for some
> size groups, e.g. nuclear power in family business.
>
>
OK, point taken. What do you think would be the best thing to do?

<snip>

Chuck
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