weka.core.UnassignedDatasetException when creating an unlabeled instance

Question

I trained an IBK classifier with some training data that I created manually as following:

ArrayList atts = new ArrayList();         


        

Answer 1

See pages 203 - 204 of the WEKA documentation. That helped me a lot! (The Weka Manual is a pdf file that is located in your weka installation folder. Just open the doucmentation.html and it will point you to the pdf manual.)

Copy-pasting some snippets of the code listings of Chapter 17 (Using the WEKA API / Creating datasets in memory) should help you solve the task.

Answer 2

The problem is with this line:

double classif = ibk.classifyInstance(newInst);

When you try to classify newInst, Weka throws an exception because newInst has no Instances object (i.e., dataset) associated with it - thus it does not know anything about its class attribute.

You should first create a new Instances object similar to the dataRaw, add your unlabeled instance to it, set class index, and only then try classifying it, e.g.:

Instances dataUnlabeled = new Instances("TestInstances", atts, 0);
dataUnlabeled.add(newInst);
dataUnlabeled.setClassIndex(dataUnlabeled.numAttributes() - 1);        
double classif = ibk.classifyInstance(dataUnlabeled.firstInstance());

Answer 3

You will see this error, when you classify a new instance which is not associated with a dataset. You have to associate every new instance you create to an Instances object using setDataset.

//Make a place holder Instances
//If you already have access to one, you can skip this step
Instances dataset = new Instances("testdata", attr, 1);
dataset.setClassIndex(classIdx);

DenseInstance newInst = new DenseInstance(1.0,values);

//To associate your instance with Instances object, in this case dataset
newInst.setDataset(dataset); 

After this you can classify newly created instance.

double classif = ibk.classifyInstance(newInst);

http://www.cs.tufts.edu/~ablumer/weka/doc/weka.core.Instance.html

Detailed Implementation Link