TokenSequenceNGrams.java

/* Copyright (C) 2002 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.Instance;
import edu.nd.nina.types.Token;
import edu.nd.nina.types.TokenSequence;

/**
 * Convert the token sequence in the data field to a token sequence of ngrams.
 * 
 * @author Don Metzler <a
 *         href="mailto:metzler@cs.umass.edu">metzler@cs.umass.edu</a>
 */

public class TokenSequenceNGrams extends Pipe{
	int[] gramSizes = null;

	public TokenSequenceNGrams(int[] sizes) {
		this.gramSizes = sizes;
	}

	public Instance pipe(Instance carrier) {
		String newTerm = null;
		TokenSequence tmpTS = new TokenSequence();
		TokenSequence ts = (TokenSequence) carrier.getData();

		for (int i = 0; i < ts.size(); i++) {
			Token t = ts.get(i);
			for (int j = 0; j < gramSizes.length; j++) {
				int len = gramSizes[j];
				if (len <= 0 || len > (i + 1))
					continue;
				if (len == 1) {
					tmpTS.add(t);
					continue;
				}
				newTerm = new String(t.getText());
				for (int k = 1; k < len; k++)
					newTerm = ts.get(i - k).getText() + "_" + newTerm;
				tmpTS.add(newTerm);
			}
		}

		carrier.setData(tmpTS);

		return carrier;
	}
}