Re: reading HDF5 slices in octave

[David Bateman]

Josselin Mouette a écrit :

> Le vendredi 04 novembre 2005 à 12:53 -0600, Quentin Spencer a écrit :
>  
>
> > > Not that this is not really a replacement for the h5read plugin, since 
> > > it only loads the entire HDF5 file.  If you want to read in a single 
> > > slice, say of a large 3d dataset, that is inconvenient (especially 
> > > since Octave doesn't support 3d arrays, unless that's changed recently).
> > >      
> > That has changed, but not very recently. It was around 2.1.52 or 53, if 
> > I recall correctly, which was released almost 2 years ago.
> >    
>
> Currently, does it work as a full replacement for h5read.oct? If this
> isn't the case, I can re-enable the plugin in h5utils.
>
> Regards,
>  
Well "load <file> <var>" should load the variable <var> from <file>. In 
the case of hdf5 files the group name is assumed to be the variable 
name. So I think we can load single variables from an hdf5 file. As for 
NDArray stuff as Quentin pointed out it was added in 2.1.53.

Note that there was also another change to hdf5 support at 2.1.53 that 
might cause some issues. To allow arbitrary types, all variables are now 
saved as a group, with a field "value" being the data and the field 
"type" being the name of the octave type. The reason for this is that 
the old way of saving hdf5 could not distinguish between say an int8 
matrix and a double matrix that just happened to be saved as an int8 
matrix. Additional, we couldn't extend the old way of saving hdf5 files 
for arbitrary octave types (sparse, galois fields, etc). This doesn't 
pose any issues when loading the file, but it does mean that octave will 
resave the data in a different format than it reads it in. So if there 
is an h5write.oct utility this might still be useful to have around...

Regards
David



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