/* 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. */
/**
@author Andrew McCallum <a href="mailto:mccallum@cs.umass.edu">mccallum@cs.umass.edu</a>
*/
package cc.mallet.pipe;
import java.io.*;
import cc.mallet.types.Instance;
import cc.mallet.types.TokenSequence;
/**
* Transform a character sequence into a token sequence of character N grams.
* @author Andrew McCallum <a href="mailto:mccallum@cs.umass.edu">mccallum@cs.umass.edu</a>
*/
public class CharSequence2CharNGrams extends Pipe implements Serializable
{
int n;
boolean distinguishBorders = false;
static char startBorderChar = '>';
static char endBorderChar = '<';
public CharSequence2CharNGrams (int n, boolean distinguishBorders)
{
this.n = n;
this.distinguishBorders = distinguishBorders;
}
protected String[] ngramify (CharSequence s)
{
if (distinguishBorders)
s = new StringBuffer().append(startBorderChar).append(s).append(endBorderChar).toString();
int count = s.length() - n;
String[] ngrams = new String[count];
for (int i = 0; i < count; i++)
ngrams[i] = s.subSequence (i, i+n).toString();
return ngrams;
}
public Instance pipe (Instance carrier)
{
if (carrier.getData() instanceof CharSequence)
carrier.setData(new TokenSequence (ngramify ((CharSequence)carrier.getData())));
else if (carrier.getData() instanceof TokenSequence) {
TokenSequence ts = (TokenSequence) carrier.getData();
TokenSequence ret = new TokenSequence ();
for (int i = 0; i < ts.size(); i++)
ret.add (ngramify (ts.get(i).getText()).toString());
carrier.setData(ret);
} else
throw new IllegalArgumentException ("Unhandled type "+carrier.getData().getClass());
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(n);
out.writeBoolean(distinguishBorders);
}
private void readObject (ObjectInputStream in) throws IOException, ClassNotFoundException {
int version = in.readInt ();
n = in.readInt();
distinguishBorders = in.readBoolean();
}
}