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 cc.mallet.pipe;


import java.io.*;

import cc.mallet.types.*;
/**
 * 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;
	}

	// Serialization

	private static final long serialVersionUID = 1;
	private static final int CURRENT_SERIAL_VERSION = 0;

	private void writeObject (ObjectOutputStream out) throws IOException {
		out.writeInt (CURRENT_SERIAL_VERSION);
		out.writeObject(biDictionary);
	}

	private void readObject (ObjectInputStream in) throws IOException, ClassNotFoundException {
		int version = in.readInt ();
		biDictionary = (Alphabet) in.readObject();
	}



}