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package com.wcohen.ss.tokens;
import java.util.*;
import com.wcohen.ss.api.*;
/**
* Wraps another tokenizer, and adds all computes all ngrams of
* characters from a single token produced by the inner tokenizer.
*/
public class NGramTokenizer implements Tokenizer
{
private int minNGramSize;
private int maxNGramSize;
private boolean keepOldTokens;
private Tokenizer innerTokenizer; // used for
public static NGramTokenizer DEFAULT_TOKENIZER = new NGramTokenizer(3,5,true,SimpleTokenizer.DEFAULT_TOKENIZER);
public NGramTokenizer(int minNGramSize,int maxNGramSize,boolean keepOldTokens,Tokenizer innerTokenizer) {
this.minNGramSize = minNGramSize;
this.maxNGramSize = maxNGramSize;
this.keepOldTokens = keepOldTokens;
this.innerTokenizer = innerTokenizer;
}
/** Return tokenized version of a string. Tokens are all
* character n-grams that are part of a token produced by the
* inner tokenizer. */
public Token[] tokenize(String input)
{
Token[] initialTokens = innerTokenizer.tokenize(input);
List tokens = new ArrayList();
for (int i=0; i<initialTokens.length; i++) {
Token tok = initialTokens[i];
String str = "^"+tok.getValue()+"$";
if (keepOldTokens) tokens.add( intern(str) );
for (int lo=0; lo<str.length(); lo++) {
for (int len=minNGramSize; len<=maxNGramSize; len++) {
if (lo+len<str.length()) {
tokens.add( innerTokenizer.intern( str.substring(lo,lo+len) ));
}
}
}
}
return (Token[]) tokens.toArray(new BasicToken[tokens.size()]);
}
public Token intern(String s) { return innerTokenizer.intern(s); }
public Iterator tokenIterator() { return innerTokenizer.tokenIterator(); }
public int maxTokenIndex() { return innerTokenizer.maxTokenIndex(); }
/** Test routine */
public static void main(String[] argv)
{
NGramTokenizer tokenizer = NGramTokenizer.DEFAULT_TOKENIZER;
//NGramTokenizer tokenizer = new NGramTokenizer(1,1,false,SimpleTokenizer.DEFAULT_TOKENIZER);
int n = 0;
for (int i=0; i<argv.length; i++) {
System.out.println("argument "+i+": '"+argv[i]+"'");
Token[] tokens = tokenizer.tokenize(argv[i]);
for (int j=0; j<tokens.length; j++) {
System.out.println("token "+(++n)+":"
+" id="+tokens[j].getIndex()
+" value: '"+tokens[j].getValue()+"'");
}
}
}
}
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