[Nexus] deleting data

[Akeroyd, FA (Freddie)]

Hi,

I had a feeling there was a technical rather than philosophical reason
for NeXus not having a "delete" function as part of the API - this may
be a leftover from early HDF4 support. It looks like it is now possible
to delete items from an HDF file, but according to
http://hdfgroup.org/hdf5-quest.html#del you do not currently get the
unused space back.

I suggest you file a ticket to http://trac.nexusformat.org/code/

Regards,

Freddie

> -----Original Message-----
> From: nexus-bounces at nexusformat.org [mailto:nexus-
> bounces at nexusformat.org] On Behalf Of Carlos Pascual Izarra
> Sent: 03 June 2009 14:08
> To: jemian at anl.gov; nexus at nexusformat.org
> Subject: Re: [Nexus] deleting data
> 
> Is it really a matter of philosophy?
> Or is there some technical limitation as well?
> 
> Because, on philosophy grounds, I would argue that some types of data
> might be
> only of temporary interest. In my case, the question comes from using
> attributes to tag data internally (I asked about this in a recent
email
> to
> the list). But I can think of other applications:  metadata that may
> change
> with analysis, or data linked from NXdata groups to construct a
default
> plot
> that is refined on a later stage of the data processing,...
> 
> The workaround of creating a new file is non-practical: what if you
are
> dealing with a huge file (e.g. a tomography experiment) in which you
> want to
> delete a single attribute?
> 
> Furthermore: it is obvious that providing the *ability* to erase data
> doesn't
> mean that someone is forced to do so. It would be an enhancement that
> some
> people may find useful, though.
> 
> So, I reformulate my question: is there a technical reason preventing
> from
> implementing data erasing?
> Maybe dealing with compression?
> 
> Cheers!
> 
> 
> On Wednesday 03 June 2009 14:35:01 Pete Jemian wrote:
> > Not a silly question.  Not a bug.
> > Instead, create a new file extracting only the wanted parts.
> > Philosophy is that the data is precious, too precious to dispose.
> >
> > Carlos Pascual Izarra wrote:
> > > Hello,
> > > This might be a silly question, but...
> > >
> > > Is there a way of deleting data (i.e., attributes, data items,
data
> > > groups and links) from a nexus file?
> > >
> > > If not: does it make sense to open a bug ticket about it?
> > >
> > > Cheers,
> 
> 
> 
> --
> +----------------------------------------------------+
>  Carlos Pascual Izarra
>  Scientific Software Contact
>  Computing Division
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