Target2Label.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.Alphabet;
import edu.nd.nina.types.Instance;
import edu.nd.nina.types.Label;
import edu.nd.nina.types.LabelAlphabet;

/**
 * Convert object in the target field into a label in the target field.
 * 
 * @author Andrew McCallum <a
 *         href="mailto:mccallum@cs.umass.edu">mccallum@cs.umass.edu</a>
 */

public class Target2Label extends Pipe {

	// gsc: adding constructor that has an option for the data alphabet as well,
	// this avoids the data alphabet getting set to null towards the end of a
	// SerialPipes object because the data alphabet might have already been set
	public Target2Label(Alphabet dataAlphabet, LabelAlphabet labelAlphabet) {
		super(dataAlphabet, labelAlphabet);
	}

	public Target2Label() {
		this(null, new LabelAlphabet());
	}

	public Target2Label(LabelAlphabet labelAlphabet) {
		this(null, labelAlphabet);
	}

	public Instance pipe(Instance carrier) {
		if (carrier.getTarget() != null) {
			if (carrier.getTarget() instanceof Label)
				throw new IllegalArgumentException("Already a label.");
			LabelAlphabet ldict = (LabelAlphabet) getTargetAlphabet();
			carrier.setTarget(ldict.lookupLabel(carrier.getTarget()));
		}
		return carrier;
	}

}