# [Numpy-discussion] rank-0 arrays

Paul F Dubois paul at pfdubois.com
Fri Sep 13 14:07:01 CDT 2002

```This is a perfect example of why the thing is so annoying.
> -----Original Message-----
> From: numpy-discussion-admin at lists.sourceforge.net
> [mailto:numpy-discussion-admin at lists.sourceforge.net] On
> Behalf Of eric jones
> Sent: Friday, September 13, 2002 1:44 PM
> To: 'Tim Hochberg'; numpy-discussion at lists.sourceforge.net
> Subject: RE: [Numpy-discussion] rank-0 arrays
>
>
> Hey Tim,
>
> Here is a short summary:
>
> Reductions and indexing return different types based on the
> number of dimensions of the input array:
>
> >>> b = sum(a)
> >>> l = len(b) # or whatever
>
> This code works happily if "a" is 2 or more dimensions, but
> will fail if it is 1d because the sum(a) will return a scalar
> in this case.  To write generic code, you have to put an
> if/else statement in to check whether b is a scalar or an array:
>
> >>> b = sum(a)
> >>> if type(b) is ArrayType:
> ...     l = len(b)
> ... else:
> ...     l = 1 # or whatever you need
>
> or less verbose but still unpleasant:
>
> >>> b = asarray(sum(a))
> >>> l = len(b)
>
> eric
>
> > -----Original Message-----
> > From: numpy-discussion-admin at lists.sourceforge.net [mailto:numpy-
> > discussion-admin at lists.sourceforge.net] On Behalf Of Tim Hochberg
> > Sent: Friday, September 13, 2002 3:18 PM
> > To: numpy-discussion at lists.sourceforge.net
> > Subject: Re: [Numpy-discussion] rank-0 arrays
> >
> >
> >
> >
> > [Perry wrote about Travis's proposal]
> >
> > > refresh my memory about how this proposal would work. I've heard
> > > proposals to add new types to Python itself, but that
> seems out of
> > > the question. Are you talking about adding new scalar types as
> > > module? E.g.
> > [snip]
> > > In any case, doesn't this still have the problem that Eric
> complained
> > > about, having to test for whether a result is an array or
> a scalar
> > > (which was one of the drivers to produce rank-0 results).
> >
> > Hi Perry,
> >
> > I like Travis's proposal the best of those I've seen so far, but I
> don't
> > recall the details of Eric's problem. Could you refresh us
> as to the
> > basics of it?.
> >
> > -tim
> >
> >
> >
> >
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```