Hi Kalpa,
Being “compound “ doesn’t really matter—that’s just the data type and size needed per record. Here is how I extend datasets—compound or otherwise.
1) Call H5D.setExtent to enlarge the extents. (http://www.hdfgroup.org/HDF5/doc/RM/RM_H5D.html#Dataset-SetExtent)
2) Close your dataspace and get it again to make sure you have the new extents
3) Use a hyperslab (H5S.selectHyperslab) to specify the destination (may be other ways, but this works for me)
4) Call H5.write – using the overload with parameters for your hyperslab dataspace. It is this dataspace that is going to tell write how/where to write the data back to the dataset.
Below is a generic function I wrote (c#, but should be similar in Java) to “append” data that extends the 1st dimension of an n-dimension array (particular to the data I work with).
The other thing I did when using compound types was to write a static method that returns a H5DataType id for the structure. You could also store this in the hdf5 file, but I haven’t done that.
Warm Regards,
Jim
private void AppendDataAny<T>(string dataSetPath, Array theData)
{
#if !HDFMT
lock (_staticObjectLock)
{
#endif
CheckOpenFile();
if (theData.Length == 0 || theData.GetUpperBound(0) == 0 || theData.Rank > 32) return;
int rank = theData.Rank;
H5DataSetId dataSetId = H5D.open(_H5FileId, dataSetPath); //Get the dataSetID based off of the data name.
H5DataSpaceId dataSpaceId = H5D.getSpace(dataSetId); //get the dataSpaceID of the dataSetID
long[] existingDataExtents = H5S.getSimpleExtentDims(dataSpaceId);
long[] newDataDims = theData.GetSize();
long[] newDataExtents = theData.GetSize();
newDataExtents[0] = existingDataExtents[0] + newDataDims[0];
H5D.setExtent(dataSetId, newDataExtents);
H5S.close(dataSpaceId);
dataSpaceId = H5D.getSpace(dataSetId);
//Allocate some memory space to hold the new data in memory during I/O
H5DataSpaceId memSpaceId = H5S.create_simple(rank, newDataDims);
//Select the area of data that we'll want to write to in the data file using a 'hyperslab'
long[] offset = new long[rank];
offset[0] = existingDataExtents[0];
long[] count = newDataDims;
H5S.selectHyperslab(dataSpaceId, H5S.SelectOperator.SET, offset, count);
//Now that we have all the pre-work figured out, we can actually write some data out.
H5DataTypeId dataTypeId = GetH5NativeType(typeof (T));
H5D.write(dataSetId, dataTypeId, memSpaceId, dataSpaceId, _defaultPropsId, new H5Array<T>(theData));
_log.DebugFormatIfEnabled("Appended data to: {0}. Offset: {1}. Data dims: {2}.", dataSetPath, existingDataExtents[0], newDataDims.PrintValues());
//Cleanup
CloseStandardTypeIds<T>(dataTypeId, memSpaceId, dataSpaceId, dataSetId);
#if !HDFMT
}
#endif
}
···
From: Hdf-forum [mailto:hdf-forum-bounces@lists.hdfgroup.org] On Behalf Of Karpaga Rajadurai
Sent: Friday, May 2, 2014 4:31 AM
To: hdf-forum@lists.hdfgroup.org
Subject: [Hdf-forum] Expanding compound dataset - Java
I created a compound dataset using the following api.
file = new H5File(FILENAME, FileFormat.CREATE);
file.open();
long[] dims = {10000, 10};
long[] maxdims = {-1, -1};
long[] chunks = {100, 10};
int gzip = 4;
Dataset d = file.createCompoundDS(FILENAME, null, dims, maxdims, chunks, gzip, memberNames, memberDatatypes, memberSizes, data);
Now, a dataset "d" of size 10000x10 is created. How to extend the created dataset?
(ie.) I want to add 10000 more rows to the dataset.
I tried using,
long[] start = dataset.getStartDims();
long[] sizes = dataset.getSelectedDims();
start[0] = 10001;
start[1] = 0;
sizes[0] = 20001;
sizes[1] = 10;
dataset.write(new_data);
I expected the dataset to get extended (from rows size to 10000 to 20000).
But instead the already written dataset is rewritten with the new_data. 
May I know what I am missing here? How to extend a compound dataset?
Thanks in advance.
Kalpa
