I don't see a reason to not write comments into the header of an ARFF file. The specification clearly says:
Lines that begin with a % are comments.
So while it is technically valid, it can be difficult if you want to use the ArffSaver#setFile
method. This method does a lot of (convenient, but somewhat arbitrary and unspecified) work internally, until it finally calls
setDestination(new FileOutputStream(m_outputFile));
If this is not required, the easiest option is to write directly to an OutputStream
, which then can simply be set as the destination for the ArffSaver
. This can be wrapped in a small helper method, for example, like this:
static void writeArff(
Instances instances,
List<String> commentLines,
OutputStream outputStream) throws IOException
{
ArffSaver saver = new ArffSaver();
saver.setInstances(instances);
if (commentLines != null && !commentLines.isEmpty())
{
BufferedWriter bw = new BufferedWriter(
new OutputStreamWriter(outputStream));
for (String commentLine : commentLines)
{
bw.write("% " + commentLine + "\n");
}
bw.write("\n");
bw.flush();
}
saver.setDestination(outputStream);
saver.writeBatch();
}
When calling it like this
List<String> comments = Arrays.asList("A comment", "Another one");
writeArff(instances, comments, outputStream);
then the given comments will be inserted at the top of the ARFF file.