MATLAB Programming

7 Working with Scientific Data Formats
c
Create the data set. In HDF5, you use the H5Dcreate routine to create
a data set. The example uses the corresponding MATLAB function,
H5D.create, specifying the file ID, the name you want to assign to
the data set, data type ID, the data space ID, and a data set creation
property list ID as arguments. The example uses the defaults for the
property lists. The function returns a data set ID.
dsetname = 'my_dataset';
datasetID = H5D.create(fileID,dsetname,datatypeID,dataspaceID,'H5P_DEFAULT');
Note To write a large data set, you must use the chunking capability
of the HDF5 library. To do this, create a property list and use the
H5P.set_chunk function to set the chunk size in the property list. In the
following example, the dimensions of the data set are dims = [2^16
2^16] and the chunk size is 1024-by-1024. You then pass the property
list as the last argument to the data set creation function, H5D.create,
instead of using the H5P_DEFAULT value.
plistID = H5P.create('H5P_DATASET_CREATE'); % create property list
chunk_size = min([1024 1024], dims); % define chunk size
H5P.set_chunk(plistID, chunk_size); % set chunk size in property list
datasetID = H5D.create(fileID, dsetname, datatypeID, dataspaceID, plistID);
4 Write the data to the data set. In HDF5, you use the H5Dwrite routine to
writedatatoadataset. TheexampleusesthecorrespondingMATLAB
function, H5D.write, specifying as arguments the data set ID, the memory
data type ID, the memory space ID, the data space ID, the transfer property
listIDandthenameoftheMATLABvariabletobewrittentothedataset.
You can use the memory data type to specify the data type used to represent
the data in the file. The example uses the constant 'H5ML_DEFAULT' which
lets the MATLAB function do an automatic mapping to HDF5 data types.
The memory data space ID and the data set’s data space ID specify to write
subsets of the data set to the file. The example uses the constant 'H5S_ALL'
to write all the data to the file and uses the default property list.
7-32