Load model and classify input using Mallet

Question

I already have a CRF trained model that I have trained using SimpleTagger.

        SimpleTagger.main(new String[] {
                "--train", "true",
                "--model-file", "/Desktop/crfmodel",
                "--threads",  "8",
                "--training-proportion", "0.8",
                "--weights", "dense",
                "--test", "lab",
//                "--orders", "2",
                "/Desktop/annotations.txt"
        });

I am planning to load this model and use it for tagging. I am using this code.

    public static void main(String[] args) throws Exception {

        //DOCS http://mallet.cs.umass.edu/classifier-devel.php

        Instance instance = getMyInstance();

        Classifier classifier = loadClassifier(Paths.get("/Desktop/crfmodel").toFile());

        Labeling labeling = classifier.classify(instance).getLabeling();
        Label l = labeling.getBestLabel();
        System.out.print(instance);
        System.out.println(l);
    }


    private static Classifier loadClassifier(File serializedFile)
            throws FileNotFoundException, IOException, ClassNotFoundException {
        ObjectInputStream ois = new ObjectInputStream (new FileInputStream(serializedFile));
        Classifier crf = (Classifier) ois.readObject();
        ois.close();

        return crf;
    }

When I try to do the above I get the following error

Exception in thread "main" java.lang.ClassCastException: cc.mallet.fst.CRF cannot be cast to cc.mallet.classify.Classifier
    at TagClassifier.loadClassifier(TagClassifier.java:77)
    at TagClassifier.main(TagClassifier.java:64)

The error is happening in line

Classifier crf = (Classifier) ois.readObject();

May I know why this is happening. Also, if there is a correct documented way to label an input using a trained model, can you please share any links/documentation? Thank you very much in advance!!!

user_791749 · Answer

I think I figured it out by looking at SimpleTagger code.

        crfModel = loadClassifier(Paths.get("/Desktop/crfmodel").toFile());
        pipe = crfModel.getInputPipe();
        pipe.setTargetProcessing(false);
        String formatted = getFormattedQuery(q);

        Instance instance = pipe.pipe(new Instance(formatted, null, null, null));
        Sequence sequence = (Sequence) instance.getData();
        Sequence[] tags = tag(sequence, 3);

    private static Sequence[] tag(Sequence input, int bestK) {
        Sequence[] answers;
        if (bestK == 1) {
            answers = new Sequence[1];
            answers[0] = crfModel.transduce(input);
        } else {
            MaxLatticeDefault lattice = new MaxLatticeDefault(crfModel, input, null);
            answers = lattice.bestOutputSequences(bestK).toArray(new Sequence[0]);
        }
        return answers;
    }

user_6287504 · Answer

They're different things, so you can't cast one to the other. A CRF infers classes for each element in a sequence, so its output is an array of labels. A classifier takes one input and returns one label.

Load model and classify input using Mallet

2 Answers