def write(filename, groupname, items, times, features, properties=None,
          dformat='dense', chunk_size='auto', sparsity=0.1, mode='a'):
    sparsity = sparsity if dformat == 'sparse' else None
    data = Data(items, times, features, properties=properties,
                sparsity=sparsity, check=True)
    Writer(filename, chunk_size=chunk_size).write(data, groupname, append=True)