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ldclakmal/Stemmer.java

Created January 21, 2018 02:47
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Stemmer, implementing the Porter Stemming Algorithm
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Stemmer.java
package DM;
/*
Porter stemmer in Java. The original paper is in
Porter, 1980, An algorithm for suffix stripping, Program, Vol. 14,
no. 3, pp 130-137,
See also http://www.tartarus.org/~martin/PorterStemmer
History:
Release 1
Bug 1 (reported by Gonzalo Parra 16/10/99) fixed as marked below.
The words 'aed', 'eed', 'oed' leave k at 'a' for step 3, and b[k-1]
is then out outside the bounds of b.
Release 2
Similarly,
Bug 2 (reported by Steve Dyrdahl 22/2/00) fixed as marked below.
'ion' by itself leaves j = -1 in the test for 'ion' in step 5, and
b[j] is then outside the bounds of b.
Release 3
Considerably revised 4/9/00 in the light of many helpful suggestions
from Brian Goetz of Quiotix Corporation ([email protected]).
Release 4
*/
import java.io.*;
/**
* Stemmer, implementing the Porter Stemming Algorithm
* <p>
* The Stemmer class transforms a word into its root form. The input
* word can be provided a character at time (by calling add()), or at once
* by calling one of the various stem(something) methods.
*/
class Stemmer {
private char[] b;
private int i, /* offset into b */
i_end, /* offset to end of stemmed word */
j, k;
private static final int INC = 50;
/* unit of size whereby b is increased */
public Stemmer() {
b = new char[INC];
i = 0;
i_end = 0;
}
/**
* Add a character to the word being stemmed. When you are finished
* adding characters, you can call stem(void) to stem the word.
*/
public void add(char ch) {
if (i == b.length) {
char[] new_b = new char[i + INC];
for (int c = 0; c < i; c++) new_b[c] = b[c];
b = new_b;
}
b[i++] = ch;
}
/**
* Adds wLen characters to the word being stemmed contained in a portion
* of a char[] array. This is like repeated calls of add(char ch), but
* faster.
*/
public void add(char[] w, int wLen) {
if (i + wLen >= b.length) {
char[] new_b = new char[i + wLen + INC];
for (int c = 0; c < i; c++) new_b[c] = b[c];
b = new_b;
}
for (int c = 0; c < wLen; c++) b[i++] = w[c];
}
/**
* After a word has been stemmed, it can be retrieved by toString(),
* or a reference to the internal buffer can be retrieved by getResultBuffer
* and getResultLength (which is generally more efficient.)
*/
public String toString() {
return new String(b, 0, i_end);
}
/**
* Returns the length of the word resulting from the stemming process.
*/
public int getResultLength() {
return i_end;
}
/**
* Returns a reference to a character buffer containing the results of
* the stemming process. You also need to consult getResultLength()
* to determine the length of the result.
*/
public char[] getResultBuffer() {
return b;
}
/* cons(i) is true <=> b[i] is a consonant. */
private final boolean cons(int i) {
switch (b[i]) {
case 'a':
case 'e':
case 'i':
case 'o':
case 'u':
return false;
case 'y':
return (i == 0) ? true : !cons(i - 1);
default:
return true;
}
}
/* m() measures the number of consonant sequences between 0 and j. if c is
a consonant sequence and v a vowel sequence, and <..> indicates arbitrary
presence,
<c><v> gives 0
<c>vc<v> gives 1
<c>vcvc<v> gives 2
<c>vcvcvc<v> gives 3
....
*/
private final int m() {
int n = 0;
int i = 0;
while (true) {
if (i > j) return n;
if (!cons(i)) break;
i++;
}
i++;
while (true) {
while (true) {
if (i > j) return n;
if (cons(i)) break;
i++;
}
i++;
n++;
while (true) {
if (i > j) return n;
if (!cons(i)) break;
i++;
}
i++;
}
}
/* vowelinstem() is true <=> 0,...j contains a vowel */
private final boolean vowelinstem() {
int i;
for (i = 0; i <= j; i++) if (!cons(i)) return true;
return false;
}
/* doublec(j) is true <=> j,(j-1) contain a double consonant. */
private final boolean doublec(int j) {
if (j < 1) return false;
if (b[j] != b[j - 1]) return false;
return cons(j);
}
/* cvc(i) is true <=> i-2,i-1,i has the form consonant - vowel - consonant
and also if the second c is not w,x or y. this is used when trying to
restore an e at the end of a short word. e.g.
cav(e), lov(e), hop(e), crim(e), but
snow, box, tray.
*/
private final boolean cvc(int i) {
if (i < 2 || !cons(i) || cons(i - 1) || !cons(i - 2)) return false;
{
int ch = b[i];
if (ch == 'w' || ch == 'x' || ch == 'y') return false;
}
return true;
}
private final boolean ends(String s) {
int l = s.length();
int o = k - l + 1;
if (o < 0) return false;
for (int i = 0; i < l; i++) if (b[o + i] != s.charAt(i)) return false;
j = k - l;
return true;
}
/* setto(s) sets (j+1),...k to the characters in the string s, readjusting
k. */
private final void setto(String s) {
int l = s.length();
int o = j + 1;
for (int i = 0; i < l; i++) b[o + i] = s.charAt(i);
k = j + l;
}
/* r(s) is used further down. */
private final void r(String s) {
if (m() > 0) setto(s);
}
/* step1() gets rid of plurals and -ed or -ing. e.g.
caresses -> caress
ponies -> poni
ties -> ti
caress -> caress
cats -> cat
feed -> feed
agreed -> agree
disabled -> disable
matting -> mat
mating -> mate
meeting -> meet
milling -> mill
messing -> mess
meetings -> meet
*/
private final void step1() {
if (b[k] == 's') {
if (ends("sses")) k -= 2;
else if (ends("ies")) setto("i");
else if (b[k - 1] != 's') k--;
}
if (ends("eed")) {
if (m() > 0) k--;
} else if ((ends("ed") || ends("ing")) && vowelinstem()) {
k = j;
if (ends("at")) setto("ate");
else if (ends("bl")) setto("ble");
else if (ends("iz")) setto("ize");
else if (doublec(k)) {
k--;
{
int ch = b[k];
if (ch == 'l' || ch == 's' || ch == 'z') k++;
}
} else if (m() == 1 && cvc(k)) setto("e");
}
}
/* step2() turns terminal y to i when there is another vowel in the stem. */
private final void step2() {
if (ends("y") && vowelinstem()) b[k] = 'i';
}
/* step3() maps double suffices to single ones. so -ization ( = -ize plus
-ation) maps to -ize etc. note that the string before the suffix must give
m() > 0. */
private final void step3() {
if (k == 0) return; /* For Bug 1 */
switch (b[k - 1]) {
case 'a':
if (ends("ational")) {
r("ate");
break;
}
if (ends("tional")) {
r("tion");
break;
}
break;
case 'c':
if (ends("enci")) {
r("ence");
break;
}
if (ends("anci")) {
r("ance");
break;
}
break;
case 'e':
if (ends("izer")) {
r("ize");
break;
}
break;
case 'l':
if (ends("bli")) {
r("ble");
break;
}
if (ends("alli")) {
r("al");
break;
}
if (ends("entli")) {
r("ent");
break;
}
if (ends("eli")) {
r("e");
break;
}
if (ends("ousli")) {
r("ous");
break;
}
break;
case 'o':
if (ends("ization")) {
r("ize");
break;
}
if (ends("ation")) {
r("ate");
break;
}
if (ends("ator")) {
r("ate");
break;
}
break;
case 's':
if (ends("alism")) {
r("al");
break;
}
if (ends("iveness")) {
r("ive");
break;
}
if (ends("fulness")) {
r("ful");
break;
}
if (ends("ousness")) {
r("ous");
break;
}
break;
case 't':
if (ends("aliti")) {
r("al");
break;
}
if (ends("iviti")) {
r("ive");
break;
}
if (ends("biliti")) {
r("ble");
break;
}
break;
case 'g':
if (ends("logi")) {
r("log");
break;
}
}
}
/* step4() deals with -ic-, -full, -ness etc. similar strategy to step3. */
private final void step4() {
switch (b[k]) {
case 'e':
if (ends("icate")) {
r("ic");
break;
}
if (ends("ative")) {
r("");
break;
}
if (ends("alize")) {
r("al");
break;
}
break;
case 'i':
if (ends("iciti")) {
r("ic");
break;
}
break;
case 'l':
if (ends("ical")) {
r("ic");
break;
}
if (ends("ful")) {
r("");
break;
}
break;
case 's':
if (ends("ness")) {
r("");
break;
}
break;
}
}
/* step5() takes off -ant, -ence etc., in context <c>vcvc<v>. */
private final void step5() {
if (k == 0) return; /* for Bug 1 */
switch (b[k - 1]) {
case 'a':
if (ends("al")) break;
return;
case 'c':
if (ends("ance")) break;
if (ends("ence")) break;
return;
case 'e':
if (ends("er")) break;
return;
case 'i':
if (ends("ic")) break;
return;
case 'l':
if (ends("able")) break;
if (ends("ible")) break;
return;
case 'n':
if (ends("ant")) break;
if (ends("ement")) break;
if (ends("ment")) break;
/* element etc. not stripped before the m */
if (ends("ent")) break;
return;
case 'o':
if (ends("ion") && j >= 0 && (b[j] == 's' || b[j] == 't')) break;
/* j >= 0 fixes Bug 2 */
if (ends("ou")) break;
return;
/* takes care of -ous */
case 's':
if (ends("ism")) break;
return;
case 't':
if (ends("ate")) break;
if (ends("iti")) break;
return;
case 'u':
if (ends("ous")) break;
return;
case 'v':
if (ends("ive")) break;
return;
case 'z':
if (ends("ize")) break;
return;
default:
return;
}
if (m() > 1) k = j;
}
/* step6() removes a final -e if m() > 1. */
private final void step6() {
j = k;
if (b[k] == 'e') {
int a = m();
if (a > 1 || a == 1 && !cvc(k - 1)) k--;
}
if (b[k] == 'l' && doublec(k) && m() > 1) k--;
}
/**
* Stem the word placed into the Stemmer buffer through calls to add().
* Returns true if the stemming process resulted in a word different
* from the input. You can retrieve the result with
* getResultLength()/getResultBuffer() or toString().
*/
public void stem() {
k = i - 1;
if (k > 1) {
step1();
step2();
step3();
step4();
step5();
step6();
}
i_end = k + 1;
i = 0;
}
/**
* Test program for demonstrating the Stemmer. It reads text from a
* a list of files, stems each word, and writes the result to standard
* output. Note that the word stemmed is expected to be in lower case:
* forcing lower case must be done outside the Stemmer class.
* Usage: Stemmer file-name file-name ...
*/
public static void main(String[] args) {
char[] w = new char[501];
Stemmer s = new Stemmer();
for (int i = 0; i < args.length; i++)
try {
FileInputStream in = new FileInputStream(args[i]);
try {
while (true) {
int ch = in.read();
if (Character.isLetter((char) ch)) {
int j = 0;
while (true) {
ch = Character.toLowerCase((char) ch);
w[j] = (char) ch;
if (j < 500) j++;
ch = in.read();
if (!Character.isLetter((char) ch)) {
/* to test add(char ch) */
for (int c = 0; c < j; c++) s.add(w[c]);
/* or, to test add(char[] w, int j) */
/* s.add(w, j); */
s.stem();
{
String u;
/* and now, to test toString() : */
u = s.toString();
/* to test getResultBuffer(), getResultLength() : */
/* u = new String(s.getResultBuffer(), 0, s.getResultLength()); */
System.out.print(u);
}
break;
}
}
}
if (ch < 0) break;
System.out.print((char) ch);
}
} catch (IOException e) {
System.out.println("error reading " + args[i]);
break;
}
} catch (FileNotFoundException e) {
System.out.println("file " + args[i] + " not found");
break;
}
}
}
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