package edu.stanford.nlp.process;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Iterator;
import java.util.function.Function;
import edu.stanford.nlp.ling.Word;
/**
* 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.
*
* @author Sepandar Kamvar (sdkamvar@stanford.edu)
*/
public class Stemmer implements Function<Word,Word> {
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.
*/
private 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;
}
/**
* 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.)
*/
@Override
public String toString() {
return new String(b, 0, i_end);
}
/* 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 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 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().
*/
private 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) throws IOException {
Stemmer s = new Stemmer();
if (args[0].equals("-file")) {
Iterator<Word> it = PTBTokenizer.newPTBTokenizer(new InputStreamReader(new FileInputStream(args[1]), "utf-8"));
while (it.hasNext()) {
Word token = it.next();
System.out.print(s.stem(token.word()));
System.out.print(' ');
}
} else {
for (String arg : args) {
System.out.print(s.stem(arg));
System.out.print(' ');
}
}
System.out.println();
}
/**
* Stems <code>s</code> and returns stemmed <code>String</code>.
*/
public String stem(String s) {
char[] characters = s.toCharArray();
for (char character : characters) {
add(character);
}
stem();
return toString();
}
/**
* Stems <code>w</code> and returns stemmed <code>Word</code>.
*/
public Word stem(Word w) {
return (new Word(stem(w.word())));
}
/**
* Stems <code>word</code> (which must be a <code>Word</code>,
* or else
* a ClassCastException will be thrown, and returns stemmed
* <code>Word</code>.
*/
public Word apply(Word word) {
return stem(word);
}
}