Thank you Jason! Actually my previous implementation was as you outlined, saving three flat arrays containing the data, the length, and the offset separately. Later I'm attracted to vlen array because I can easily view them in hdfview and can load them as record arrays in h5py which are more user-friendly when I try to inspect the data. Saving them as separate arrays will require some wrapping later on to get convenient access.
Since this post has probably been held for quite a while by the moderating process, I have found a work-around which may not be optimal: (posted here http://stackoverflow.com/questions/33041977/only-read-the-length-of-variable-length-array-without-reading-the-elements-in-hd ) hsize_t dim[1];VarLenType vl_t(PredType:NATIVE_INT);DataSpace dspace=dset.getSpace(); dspace.getSimpleExtentDims(dim);hsize_t count[]={1}, offset[]={0}, stride[]={1}, block[]={1};for(offset[0]=0;offset[0]<dim[0];offset[0]++){ dspace.selectHyperslab(H5S_SELECT_SET, count, offset, stride, block); cout<<dset.getVlenBufSize(vl_t, dspace)/vl_t.getSuper().getSize()<<" ";} Jiaxin 2015-10-14 2:56 GMT+01:00 Jason Newton <[email protected]>: > Hi, > > Personal experience here but I think you'll come to the same conclusions > if you go through the mailing lists long enough: vlens are not a first > class citizen in HDF. There's all kinds of exceptions and requirements to > use them not common to other types. > > But what are you going to do, not have variable length data? Sheesh, > right? > > So you need to do something several dub as "linearization" - keeping a > dataset of the counts of the variable-length data in one dataset. Then > another dataset that has each of those variable-length lists concatenated > in the same order. Exclusive-prefix sum (a variant cumulative sum) that > and you'll have the starting indices of each list. > > It's a little awkward - but it works, is supported in all the > bindings/languages, and filters work on it - all of which can't be said for > vlen types. > > Of course your exact question you didn't ask this - but I'll be quick and > point out you'd have a dataset of them in the above approach that you could > load, if that's something you control. > > -Jason > > On Fri, Oct 9, 2015 at 12:38 PM, Jiaxin Han <[email protected]> wrote: > >> Hi Everyone, >> >> Is it possible to do this? >> >> I have an array containing Nvl variable length arrays already written to >> a hdf5 file. I can read in the entire data by (e.g., in c++) >> >> hvl_t vl[Nvl]; >> dset.read(vl, VarLenType(&PredType:NATIVE_INT)); >> >> However, if I only want to read the length of each variable-length >> object, i.e., vl[].len, how can I do it without reading in the data >> vl[].p as well? >> Thanks! >> >> Jiaxin >> >> >> _______________________________________________ >> Hdf-forum is for HDF software users discussion. >> [email protected] >> http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org >> Twitter: https://twitter.com/hdf5 >> > > > _______________________________________________ > Hdf-forum is for HDF software users discussion. > [email protected] > http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org > Twitter: https://twitter.com/hdf5 >
_______________________________________________ Hdf-forum is for HDF software users discussion. [email protected] http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org Twitter: https://twitter.com/hdf5
