Re: 0-rank arrays?

• To: netcdf-hdf@xxxxxxxxxxxxxxxx
• Subject: Re: 0-rank arrays?
• From: Quincey Koziol <koziol@xxxxxxxxxxxxx>
• Date: Fri, 8 Aug 2003 08:37:30 -0500 (CDT)

Hi Russ,
    Sorry for the delays in replying as I'm catching up on e-mail after
vacation.
    I don't think a rank-0 array datatype would be a really good change.
Perhaps changing  the dataspace (which can have a rank of 0) for the attribute
would be more appropriate?

    Quincey

> We're developing an alternative straw-person draft of mapping netCDF
> to HDF5, at least for the first deliverable of netCDF-3 on HDF5.
> 
> Currently, we're thinking of storing the netCDF dimension IDs for a
> netCDF variable in an HDF5 array attribute, _ncdimids, associated with
> the HDF5 dataset corresponding to the variable.  This works fine for
> array variables, but scalar (rank 0) netCDF variables have no
> associated dimension IDs.
> 
> Various ways to encode this in HDF5 include:
> 
>  - no _ncdimids attribute for scalar variables
>    
>  - an _ncdimids attribute that is not an array
> 
>  - a rank-0 _ndimids array attribute.  In this case, the rank of
>    _ncdimids would always correspond to the rank of the associated
>    variable, whether scalar or dimensioned.
> 
> The latter is not currently possible in HDF5, but would be if rank-0
> arrays were supported.  
> 
> I don't know how disruptive it would be to permit rank-0 arrays as a
> Datatype, so if it has lots of unpleasant side effects, please just
> ignore this minor request.  But if it's relatively easy, you might
> find other uses for rank-0 arrays, for example, as something to return
> to represent an empty result of a query that typically returns an
> array.  We've found that treating rank-k multidimensional arrays
> pretty much the same for k = 0, 1, 2, ... makes some code simpler.
> 
> --Russ
> 

• References:
  • 0-rank arrays?
    • From: Russ Rew