Tokenize, remove stop words using Lucene with Java

Question

I am trying to tokenize and remove stop words from a txt file with Lucene. I have this:

public String removeStopWords(String string) throws IOException {

Set<String> stopWords = new HashSet<String>();
    stopWords.add("a");
    stopWords.add("an");
    stopWords.add("I");
    stopWords.add("the");

    TokenStream tokenStream = new StandardTokenizer(Version.LUCENE_43, new StringReader(string));
    tokenStream = new StopFilter(Version.LUCENE_43, tokenStream, stopWords);

    StringBuilder sb = new StringBuilder();

    CharTermAttribute token = tokenStream.getAttribute(CharTermAttribute.class);
    while (tokenStream.incrementToken()) {
        if (sb.length() > 0) {
            sb.append(" ");
        }
        sb.append(token.toString());
    System.out.println(sb);    
    }
    return sb.toString();
}}

My main looks like this:

    String file = "..../datatest.txt";

    TestFileReader fr = new TestFileReader();
    fr.imports(file);
    System.out.println(fr.content);

    String text = fr.content;

    Stopwords stopwords = new Stopwords();
    stopwords.removeStopWords(text);
    System.out.println(stopwords.removeStopWords(text));

This is giving me an error but I can't figure out why.

Answer 1

I had The same problem. To remove stop-words using Lucene you could either use their Default Stop Set using the method EnglishAnalyzer.getDefaultStopSet();. Otherwise, you could create your own custom stop-words list.

The code below shows the correct version of your removeStopWords():

public static String removeStopWords(String textFile) throws Exception {
    CharArraySet stopWords = EnglishAnalyzer.getDefaultStopSet();
    TokenStream tokenStream = new StandardTokenizer(Version.LUCENE_48, new StringReader(textFile.trim()));

    tokenStream = new StopFilter(Version.LUCENE_48, tokenStream, stopWords);
    StringBuilder sb = new StringBuilder();
    CharTermAttribute charTermAttribute = tokenStream.addAttribute(CharTermAttribute.class);
    tokenStream.reset();
    while (tokenStream.incrementToken()) {
        String term = charTermAttribute.toString();
        sb.append(term + " ");
    }
    return sb.toString();
}

To use a custom list of stop words use the following:

//CharArraySet stopWords = EnglishAnalyzer.getDefaultStopSet(); //this is Lucene set 
final List<String> stop_Words = Arrays.asList("fox", "the");
final CharArraySet stopSet = new CharArraySet(Version.LUCENE_48, stop_Words, true);