+ * 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;
+ }
+}