featuresequence.java

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/* 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.umass.cs.mallet.base.types;

import java.util.Arrays;
import java.io.*;

/**
 *   An implementation of {@link Sequence} that ensures that every
 *   Object in the sequence has the same class.  Feature sequences are
 *   mutable, and will expand as new objects are added.
 *
 *  @author Andrew McCallum <a href="mailto:[e-mail]">[e-mail]</a>
 */

public class FeatureSequence implements Sequence, Serializable
{
	Alphabet dictionary;
	int[] features;
	int length;

	/**
	 *  Creates a FeatureSequence given all of the objects in the
	 *  sequence.
	 *
	 *  @param dict A dictionary that maps objects in the sequence
	 *     to numeric indices.
	 *  @param features An array where features[i] gives the index
	 *     in dict of the ith element of the sequence.
	 */
	public FeatureSequence (Alphabet dict, int[] features)
	{
		this(dict, features.length);
		for (int i = 0; i < features.length; i++)
			add(features[i]);
	}
	
	public FeatureSequence (Alphabet dict, int capacity)
	{
		dictionary = dict;
		features = new int[capacity > 2 ? capacity : 2];
		length = 0;
	}

	public FeatureSequence (Alphabet dict)
	{
		this (dict, 2);
	}
	
	public Alphabet getAlphabet ()	{	return dictionary; }

	public int getLength () { return length; }

	public int size () { return length; }

	public int getIndexAtPosition (int pos)
	{
		return features[pos];
	}

	public Object getObjectAtPosition (int pos)
	{
		return dictionary.lookupObject (features[pos]);
	}

	// xxx This method name seems a bit ambiguous?
	public Object get (int pos)
	{
		return dictionary.lookupObject (features[pos]);
	}

	public String toString ()
	{
		StringBuffer sb = new StringBuffer ();
		for (int fsi = 0; fsi < length; fsi++) {
			Object o = dictionary.lookupObject(features[fsi]);
			sb.append (o.toString());
			sb.append (" (");
			sb.append (features[fsi]);
			sb.append (")\n");
		}
		return sb.toString();
	}

	private void growIfNecessary ()
	{
		if (length == features.length) {
			int[] newFeatures = new int[features.length * 2];
			System.arraycopy (features, 0, newFeatures, 0, length);
			features = newFeatures;
		}
	}

	public void add (int featureIndex)
	{
		growIfNecessary ();
		assert (featureIndex < dictionary.size());
		features[length++] = featureIndex;
	}

	public void add (Object key)
	{
		int fi = dictionary.lookupIndex (key);
		if (fi >= 0)
			// This will happen if the dictionary is frozen,
			// and key is not already in the dictionary.
			add (fi);
		// xxx Should we raise an exception if the appending doesn't happen?
	}

	public void addFeatureWeightsTo (double[] weights)
	{
		for (int i = 0; i < length; i++)
			weights[features[i]]++;
	}

	public void addFeatureWeightsTo (double[] weights, double scale)
	{
		for (int i = 0; i < length; i++)
			weights[features[i]] += scale;
	}

	public int[] toFeatureIndexSequence ()
	{
		int[] feats = new int[length];
		System.arraycopy (features, 0, feats, 0, length);
		return feats;
	}

	public int[] toSortedFeatureIndexSequence ()
	{
		int[] feats = this.toFeatureIndexSequence ();
		java.util.Arrays.sort (feats);
		return feats;
	}


	// Serialization
		
	private static final long serialVersionUID = 1;
	private static final int CURRENT_SERIAL_VERSION = 0;
	private static final int NULL_INTEGER = -1;
	
	private void writeObject (ObjectOutputStream out) throws IOException {
		out.writeInt (CURRENT_SERIAL_VERSION);
		out.writeObject (dictionary);
		out.writeInt (features.length);
		for (int i = 0; i < features.length; i++)
			out.writeInt (features[i]);
		out.writeInt (length);
	}
	
	private void readObject (ObjectInputStream in) throws IOException, ClassNotFoundException {
		int featuresLength;
		int version = in.readInt ();
		dictionary = (Alphabet) in.readObject ();
		featuresLength = in.readInt();
		features = new int[featuresLength];
		for (int i = 0; i < featuresLength; i++)
			features[i] = in.readInt ();
		length = in.readInt ();
	}
	
}