lucene/analysis/common/src/java/org/apache/lucene/analysis/id/IndonesianStemmer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.lucene.analysis.id;


import static org.apache.lucene.analysis.util.StemmerUtil.*;

/**
 * Stemmer for Indonesian.
 * <p>
 * Stems Indonesian words with the algorithm presented in:
 * <i>A Study of Stemming Effects on Information Retrieval in 
 * Bahasa Indonesia</i>, Fadillah Z Tala.
 * http://www.illc.uva.nl/Publications/ResearchReports/MoL-2003-02.text.pdf
 */
public class IndonesianStemmer {
  private int numSyllables;
  private int flags;
  private static final int REMOVED_KE = 1;
  private static final int REMOVED_PENG = 2;
  private static final int REMOVED_DI = 4;
  private static final int REMOVED_MENG = 8;
  private static final int REMOVED_TER = 16;
  private static final int REMOVED_BER = 32;
  private static final int REMOVED_PE = 64;
  
  /**
   * Stem a term (returning its new length).
   * <p>
   * Use <code>stemDerivational</code> to control whether full stemming
   * or only light inflectional stemming is done.
   */
  public int stem(char text[], int length, boolean stemDerivational) {
    flags = 0;
    numSyllables = 0;
    for (int i = 0; i < length; i++)
      if (isVowel(text[i]))
          numSyllables++;
    
    if (numSyllables > 2) length = removeParticle(text, length);
    if (numSyllables > 2) length = removePossessivePronoun(text, length);
    
    if (stemDerivational)
      length = stemDerivational(text, length);
    return length;
  }
  
  private int stemDerivational(char text[], int length) {
    int oldLength = length;
    if (numSyllables > 2) length = removeFirstOrderPrefix(text, length);
    if (oldLength != length) { // a rule is fired
      oldLength = length;
      if (numSyllables > 2) length = removeSuffix(text, length);
      if (oldLength != length) // a rule is fired
        if (numSyllables > 2) length = removeSecondOrderPrefix(text, length);
    } else { // fail
      if (numSyllables > 2) length = removeSecondOrderPrefix(text, length);
      if (numSyllables > 2) length = removeSuffix(text, length);
    }
    return length;
  }
  
  private boolean isVowel(char ch) {
    switch(ch) {
      case 'a':
      case 'e':
      case 'i':
      case 'o':
      case 'u':
        return true;
      default:
        return false;
    }
  }
  
  private int removeParticle(char text[], int length) {
    if (endsWith(text, length, "kah") || 
        endsWith(text, length, "lah") || 
        endsWith(text, length, "pun")) {
        numSyllables--;
        return length - 3;
    }
    
    return length;
  }
  
  private int removePossessivePronoun(char text[], int length) {
    if (endsWith(text, length, "ku") || endsWith(text, length, "mu")) {
      numSyllables--;
      return length - 2;
    }
    
    if (endsWith(text, length, "nya")) {
      numSyllables--;
      return length - 3;
    }
    
    return length;
  }
  
  private int removeFirstOrderPrefix(char text[], int length) {
    if (startsWith(text, length, "meng")) {
      flags |= REMOVED_MENG;
      numSyllables--;
      return deleteN(text, 0, length, 4);
    }
    
    if (startsWith(text, length, "meny") && length > 4 && isVowel(text[4])) {
      flags |= REMOVED_MENG;
      text[3] = 's';
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (startsWith(text, length, "men")) {
      flags |= REMOVED_MENG;
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
 
    if (startsWith(text, length, "mem")) {
      flags |= REMOVED_MENG;
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (startsWith(text, length, "me")) {
      flags |= REMOVED_MENG;
      numSyllables--;
      return deleteN(text, 0, length, 2);
    }
    
    if (startsWith(text, length, "peng")) {
      flags |= REMOVED_PENG;
      numSyllables--;
      return deleteN(text, 0, length, 4);
    }
    
    if (startsWith(text, length, "peny") && length > 4 && isVowel(text[4])) {
      flags |= REMOVED_PENG;
      text[3] = 's';
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (startsWith(text, length, "peny")) {
      flags |= REMOVED_PENG;
      numSyllables--;
      return deleteN(text, 0, length, 4);
    }
    
    if (startsWith(text, length, "pen") && length > 3 && isVowel(text[3])) {
      flags |= REMOVED_PENG;
      text[2] = 't';
      numSyllables--;
      return deleteN(text, 0, length, 2);
    }

    if (startsWith(text, length, "pen")) {
      flags |= REMOVED_PENG;
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (startsWith(text, length, "pem")) {
      flags |= REMOVED_PENG;
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (startsWith(text, length, "di")) {
      flags |= REMOVED_DI;
      numSyllables--;
      return deleteN(text, 0, length, 2);
    }
    
    if (startsWith(text, length, "ter")) {
      flags |= REMOVED_TER;
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (startsWith(text, length, "ke")) {
      flags |= REMOVED_KE;
      numSyllables--;
      return deleteN(text, 0, length, 2);
    }
    
    return length;
  }
  
  private int removeSecondOrderPrefix(char text[], int length) {
    if (startsWith(text, length, "ber")) {
      flags |= REMOVED_BER;
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (length == 7 && startsWith(text, length, "belajar")) {
      flags |= REMOVED_BER;
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (startsWith(text, length, "be") && length > 4 
        && !isVowel(text[2]) && text[3] == 'e' && text[4] == 'r') {
      flags |= REMOVED_BER;
      numSyllables--;
      return deleteN(text, 0, length, 2);
    }
    
    if (startsWith(text, length, "per")) {
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (length == 7 && startsWith(text, length, "pelajar")) {
      numSyllables--;
      return deleteN(text, 0, length, 3);
    }
    
    if (startsWith(text, length, "pe")) {
      flags |= REMOVED_PE;
      numSyllables--;
      return deleteN(text, 0, length, 2);
    }

    return length;
  }
  
  private int removeSuffix(char text[], int length) {
    if (endsWith(text, length, "kan") 
        && (flags & REMOVED_KE) == 0 
        && (flags & REMOVED_PENG) == 0 
        && (flags & REMOVED_PE) == 0) {
      numSyllables--;
      return length - 3;
    }
    
    if (endsWith(text, length, "an") 
        && (flags & REMOVED_DI) == 0 
        && (flags & REMOVED_MENG) == 0 
        && (flags & REMOVED_TER) == 0) {
      numSyllables--;
      return length - 2;
    }
    
    if (endsWith(text, length, "i") 
        && !endsWith(text, length, "si") 
        && (flags & REMOVED_BER) == 0 
        && (flags & REMOVED_KE) == 0 
        && (flags & REMOVED_PENG) == 0) {
      numSyllables--;
      return length - 1;
    }
    return length;
  }  
}