TokenSequence2FeatureSequenceWithBigrams.java

/* Copyright (C) 2005 Univ. of Massachusetts Amherst, Computer Science Dept.
   This file is part of "MALLET" (MAchine Learning for LanguagE Toolkit).
   http://www.cs.umass.edu/~mccallum/mallet
   This software is provided under the terms of the Common Public License,
   version 1.0, as published by http://www.opensource.org.  For further
   information, see the file `LICENSE' included with this distribution. */

package edu.nd.nina.graph.load;

import edu.nd.nina.types.Alphabet;
import edu.nd.nina.types.FeatureSequence;
import edu.nd.nina.types.FeatureSequenceWithBigrams;
import edu.nd.nina.types.Instance;
import edu.nd.nina.types.TokenSequence;

/**
 * Convert the token sequence in the data field of each instance to a feature
 * sequence that preserves bigram information.
 * 
 * @author Andrew McCallum <a
 *         href="mailto:mccallum@cs.umass.edu">mccallum@cs.umass.edu</a>
 */

public class TokenSequence2FeatureSequenceWithBigrams extends Pipe {
	Alphabet biDictionary;

	public TokenSequence2FeatureSequenceWithBigrams(Alphabet dataDict,
			Alphabet bigramAlphabet) {
		super(dataDict, null);
		biDictionary = bigramAlphabet;
	}

	public TokenSequence2FeatureSequenceWithBigrams(Alphabet dataDict) {
		super(dataDict, null);
		biDictionary = new Alphabet();
	}

	public TokenSequence2FeatureSequenceWithBigrams() {
		super(new Alphabet(), null);
		biDictionary = new Alphabet();
	}

	public Alphabet getBigramAlphabet() {
		return biDictionary;
	}

	public Instance pipe(Instance carrier) {
		TokenSequence ts = (TokenSequence) carrier.getData();
		FeatureSequence ret = new FeatureSequenceWithBigrams(getDataAlphabet(),
				biDictionary, ts);
		carrier.setData(ret);
		return carrier;
	}

}