How to train Chunker in Opennlp?

Question

I need to train the Chunker in Opennlp to classify the training data as a noun phrase. How do I proceed? The documentation online does not have an explanation how to do it without the command line, incorporated in a program. It says to use en-chunker.train, but how do you make that file?

EDIT: @Alaye After running the code you gave in your answer, I get the following error that I cannot fix:

Indexing events using cutoff of 5

    Computing event counts...  done. 3 events
Dropped event B-NP:[w_2=bos, w_1=bos, w0=He, w1=reckons, w2=., w_1=bosw0=He, w0=Hew1=reckons, t_2=bos, t_1=bos, t0=PRP, t1=VBZ, t2=., t_2=bost_1=bos, t_1=bost0=PRP, t0=PRPt1=VBZ, t1=VBZt2=., t_2=bost_1=bost0=PRP, t_1=bost0=PRPt1=VBZ, t0=PRPt1=VBZt2=., p_2=bos, p_1=bos, p_2=bosp_1=bos, p_1=bost_2=bos, p_1=bost_1=bos, p_1=bost0=PRP, p_1=bost1=VBZ, p_1=bost2=., p_1=bost_2=bost_1=bos, p_1=bost_1=bost0=PRP, p_1=bost0=PRPt1=VBZ, p_1=bost1=VBZt2=., p_1=bost_2=bost_1=bost0=PRP, p_1=bost_1=bost0=PRPt1=VBZ, p_1=bost0=PRPt1=VBZt2=., p_1=bosw_2=bos, p_1=bosw_1=bos, p_1=bosw0=He, p_1=bosw1=reckons, p_1=bosw2=., p_1=bosw_1=bosw0=He, p_1=bosw0=Hew1=reckons]
Dropped event B-VP:[w_2=bos, w_1=He, w0=reckons, w1=., w2=eos, w_1=Hew0=reckons, w0=reckonsw1=., t_2=bos, t_1=PRP, t0=VBZ, t1=., t2=eos, t_2=bost_1=PRP, t_1=PRPt0=VBZ, t0=VBZt1=., t1=.t2=eos, t_2=bost_1=PRPt0=VBZ, t_1=PRPt0=VBZt1=., t0=VBZt1=.t2=eos, p_2=bos, p_1=B-NP, p_2=bosp_1=B-NP, p_1=B-NPt_2=bos, p_1=B-NPt_1=PRP, p_1=B-NPt0=VBZ, p_1=B-NPt1=., p_1=B-NPt2=eos, p_1=B-NPt_2=bost_1=PRP, p_1=B-NPt_1=PRPt0=VBZ, p_1=B-NPt0=VBZt1=., p_1=B-NPt1=.t2=eos, p_1=B-NPt_2=bost_1=PRPt0=VBZ, p_1=B-NPt_1=PRPt0=VBZt1=., p_1=B-NPt0=VBZt1=.t2=eos, p_1=B-NPw_2=bos, p_1=B-NPw_1=He, p_1=B-NPw0=reckons, p_1=B-NPw1=., p_1=B-NPw2=eos, p_1=B-NPw_1=Hew0=reckons, p_1=B-NPw0=reckonsw1=.]
Dropped event O:[w_2=He, w_1=reckons, w0=., w1=eos, w2=eos, w_1=reckonsw0=., w0=.w1=eos, t_2=PRP, t_1=VBZ, t0=., t1=eos, t2=eos, t_2=PRPt_1=VBZ, t_1=VBZt0=., t0=.t1=eos, t1=eost2=eos, t_2=PRPt_1=VBZt0=., t_1=VBZt0=.t1=eos, t0=.t1=eost2=eos, p_2B-NP, p_1=B-VP, p_2B-NPp_1=B-VP, p_1=B-VPt_2=PRP, p_1=B-VPt_1=VBZ, p_1=B-VPt0=., p_1=B-VPt1=eos, p_1=B-VPt2=eos, p_1=B-VPt_2=PRPt_1=VBZ, p_1=B-VPt_1=VBZt0=., p_1=B-VPt0=.t1=eos, p_1=B-VPt1=eost2=eos, p_1=B-VPt_2=PRPt_1=VBZt0=., p_1=B-VPt_1=VBZt0=.t1=eos, p_1=B-VPt0=.t1=eost2=eos, p_1=B-VPw_2=He, p_1=B-VPw_1=reckons, p_1=B-VPw0=., p_1=B-VPw1=eos, p_1=B-VPw2=eos, p_1=B-VPw_1=reckonsw0=., p_1=B-VPw0=.w1=eos]
    Indexing...  done.
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.rangeCheck(ArrayList.java:653)
    at java.util.ArrayList.get(ArrayList.java:429)
    at opennlp.tools.ml.model.AbstractDataIndexer.sortAndMerge(AbstractDataIndexer.java:89)
    at opennlp.tools.ml.model.TwoPassDataIndexer.<init>(TwoPassDataIndexer.java:105)
    at opennlp.tools.ml.AbstractEventTrainer.getDataIndexer(AbstractEventTrainer.java:74)
    at opennlp.tools.ml.AbstractEventTrainer.train(AbstractEventTrainer.java:91)
    at opennlp.tools.ml.model.TrainUtil.train(TrainUtil.java:53)
at opennlp.tools.chunker.ChunkerME.train(ChunkerME.java:253)
at com.oracle.crm.nlp.CustomChunker2.main(CustomChunker2.java:91)
Sorting and merging events... Process exited with exit code 1.

(My en-chunker.train had only the first 2 and last line of your sample data set.) Could you please tell me why this is happening and how to fix it?

EDIT2: I got the Chunker to work, however it gives an error when I change the sentence in the training set to any sentence other than the one you've given in your answer. Can you tell me why that could be happening?

Answer 1

As said in Opennlp Documentation

Sample sentence of the training data:

He        PRP  B-NP
reckons   VBZ  B-VP
the       DT   B-NP
current   JJ   I-NP
account   NN   I-NP
deficit   NN   I-NP
will      MD   B-VP
narrow    VB   I-VP
to        TO   B-PP
only      RB   B-NP
#         #    I-NP
1.8       CD   I-NP
billion   CD   I-NP
in        IN   B-PP
September NNP  B-NP
.         .    O

This is how you make your en-chunk.train file and you can create the corresponding .bin file using CLI:

$ opennlp ChunkerTrainerME -model en-chunker.bin -lang en -data en-chunker.train -encoding

or using API

public class SentenceTrainer {
   public static void trainModel(String inputFile, String modelFile)
  throws IOException {
  Objects.nonNull(inputFile);
  Objects.nonNull(modelFile);

      MarkableFileInputStreamFactory factory = new MarkableFileInputStreamFactory(
        new File(inputFile));


    Charset charset = Charset.forName("UTF-8");
    ObjectStream<String> lineStream =
        new PlainTextByLineStream(new FileInputStream("en-chunker.train"),charset);
    ObjectStream<ChunkSample> sampleStream = new ChunkSampleStream(lineStream);

    ChunkerModel model;

    try {
      model = ChunkerME.train("en", sampleStream,
          new DefaultChunkerContextGenerator(), TrainingParameters.defaultParams());
    }
    finally {
      sampleStream.close();
    }

    OutputStream modelOut = null;
    try {
      modelOut = new BufferedOutputStream(new FileOutputStream(modelFile));
      model.serialize(modelOut);
    } finally {
      if (modelOut != null)
         modelOut.close();
      }
     }
    }

and the main method will be:

public class Main {

public static void main(String args[]) throws IOException {
  String inputFile = "//path//to//data.train";
  String modelFile = "//path//to//.bin";

  SentenceTrainer.trainModel(inputFile, modelFile);
 }
}

reference: this blog

hope this helps!

PS: collect/write the data as above in a .txt file and rename it with .train extension or even the trainingdata.txt will work. that is how you make a .train file.