org.apache.lucene.analysis.id.IndonesianStemmer Maven / Gradle / Ivy
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* 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.
*
* Stems Indonesian words with the algorithm presented in:
* A Study of Stemming Effects on Information Retrieval in
* Bahasa Indonesia, 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).
*
* Use stemDerivational 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;
}
}