Issue with Weka core DenseInstance - weka

Question

I'm building up an Instances object, adding Attributes, and then adding data in the form of Instance objects.
When I go to write it out, the toString() method is already throwing an OutOfBoundsException and unable to evaluate the data in the Instances. I receive the error when I try to print out the data and I can see the exception being thrown just in the Debugger as it shows it can't evaluate the toString() for the data object.
The only clue I have is that the error message seems to be using the first data element (StudentId) and using it as an index. I'm confused as to why.
The code:
// Set up the attributes for the Weka data model
ArrayList<Attribute> attributes = new ArrayList<>();
attributes.add(new Attribute("StudentIdentifier", true));
attributes.add(new Attribute("CourseGrade", true));
attributes.add(new Attribute("CourseIdentifier"));
attributes.add(new Attribute("Term", true));
attributes.add(new Attribute("YearCourseTaken", true));
// Create the data model object - I'm not happy that capacity is required and fixed? But that's another issue
Instances dataSet = new Instances("Records", attributes, 500);
// Set the attribute that will be used for prediction purposes - that will be CourseIdentifier
dataSet.setClassIndex(2);
// Pull back all the records in this term range, create Weka Instance objects for each and add to the data set
List<Record> records = recordsInTermRangeFindService.find(0, 10);
int count = 0;
for (Record r : records) {
Instance i = new DenseInstance(attributes.size());
i.setValue(attributes.get(0), r.studentIdentifier);
i.setValue(attributes.get(1), r.courseGrade);
i.setValue(attributes.get(2), r.courseIdentifier);
i.setValue(attributes.get(3), r.term);
i.setValue(attributes.get(4), r.yearCourseTaken);
dataSet.add(i);
}
System.out.println(dataSet.size());
BufferedWriter writer = null;
try {
writer = new BufferedWriter(new FileWriter("./test.arff"));
writer.write(dataSet.toString());
writer.flush();
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
The error message:
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 1010, Size: 0

Answer 1

I figured it out finally. I was setting the Attributes to strings with the 'true' second parameter in the Constructors, but they were integers coming out of the database table. I needed to change my lines to convert the integers to strings:
i.setValue(attributes.get(0), Integer.toString(r.studentIdentifier));
However, that created a different set of issues for me as things like the Apriori algorithm don't work on strings! I'm continuing to plug along learning Weka.