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 * (the "License"); you may not use this file except in compliance with
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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

/** * 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).

Use stemDerivational to control whether full stemming or only light inflectional stemming is done.

/** * 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; } }