/* 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 cc.mallet.pipe;
import java.io.*;
import cc.mallet.types.Instance;
import cc.mallet.types.Token;
import cc.mallet.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 implements Serializable
{
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;
}
// 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.writeInt (gramSizes.length);
for (int i = 0; i < gramSizes.length; i++)
out.writeInt (gramSizes[i]);
}
private void readObject (ObjectInputStream in) throws IOException, ClassNotFoundException {
int version = in.readInt ();
int size = in.readInt();
gramSizes = new int[size];
for (int i = 0; i < size; i++)
gramSizes[i] = in.readInt();
}
}