Written by
彭一
on
on
java常用工具-PorterStemmer
在搜索引擎的索引和检索场景中，在自然语言处理（NLP） 场景，需要将单词还原为“词干”形式。而PorterStemmer 是 Java 中常用的 词干提取工具，它的作用:
- connection → connect
- connected → connect
- connecting → connect
- connections → connect
在 Lucene 中，就提供了这样的一个java文件。
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import StringUtil;
/**
* Copyright 2004 The Apache Software Foundation
* <p>
* Licensed 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
* <p>
* http://www.apache.org/licenses/LICENSE-2.0
* <p>
* 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.
*/
/*
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/index.html
Bug 1 (reported by Gonzalo Parra 16/10/99) fixed as marked below.
Tthe words 'aed', 'eed', 'oed' leave k at 'a' for step 3, and b[k-1]
is then out outside the bounds of b.
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.
[ This version is derived from Release 3, modified by Brian Goetz to
optimize for fewer object creations. ]
*/
/**
* Stemmer, implementing the Porter Stemming Algorithm 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.
*/
public class PorterStemmer {
private char[] b;
private int i, /* offset into b */
j, k, k0;
private boolean dirty = false;
private static final int INC = 50; /* unit of size whereby b is increased */
private static final int EXTRA = 1;
public PorterStemmer() {
b = new char[INC];
i = 0;
}
/**
* reset() resets the stemmer so it can stem another word. If you invoke the stemmer by calling add(char) and then stem(), you must call reset() before
* starting another word.
*/
public void reset() {
i = 0;
dirty = false;
}
/**
* Add a character to the word being stemmed. When you are finished adding characters, you can call stem(void) to process the word.
*/
public void add(char ch) {
if (b.length <= i + EXTRA) {
char[] new_b = new char[b.length + INC];
for (int c = 0; c < b.length; 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.)
*/
public String toString() {
return new String(b, 0, i);
}
/**
* Returns the length of the word resulting from the stemming process.
*/
public int getResultLength() {
return i;
}
/**
* 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 == k0) ? true : !cons(i - 1);
default:
return true;
}
}
/*
* m() measures the number of consonant sequences between k0 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 = k0;
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 <=> k0,...j contains a vowel */
private final boolean vowelinstem() {
int i;
for (i = k0; 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 < k0 + 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 < k0 + 2 || !cons(i) || cons(i - 1) || !cons(i - 2))
return false;
else {
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 < k0)
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.
*/
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;
dirty = true;
}
/* r(s) is used further down. */
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)) {
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';
dirty = true;
}
}
/*
* 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 == k0)
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 == k0)
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 a word provided as a String. Returns the result as a String.
*/
public String stem(String s) {
if (stem(s.toCharArray(), s.length()))
return toString();
else
return s;
}
/**
* Stem a word contained in a char[]. 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 boolean stem(char[] word) {
return stem(word, word.length);
}
/**
* Stem a word contained in a portion of a char[] array. 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 boolean stem(char[] wordBuffer, int offset, int wordLen) {
reset();
if (b.length < wordLen) {
char[] new_b = new char[wordLen + EXTRA];
b = new_b;
}
for (int j = 0; j < wordLen; j++)
b[j] = wordBuffer[offset + j];
i = wordLen;
return stem(0);
}
/**
* Stem a word contained in a leading portion of a char[] array. 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 boolean stem(char[] word, int wordLen) {
return stem(word, 0, wordLen);
}
/**
* 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 boolean stem() {
return stem(0);
}
public boolean stem(int i0) {
k = i - 1;
k0 = i0;
if (k > k0 + 1) {
step1();
step2();
step3();
step4();
step5();
step6();
}
// Also, a word is considered dirty if we lopped off letters
// Thanks to Ifigenia Vairelles for pointing this out.
if (i != k + 1)
dirty = true;
i = k + 1;
return dirty;
}
/**
* Test program for demonstrating the Stemmer. It reads a file and stems each word, writing the result to standard out. Usage: Stemmer file-name
*
* @throws IOException
*/
public static void main(String[] args) throws IOException {
PorterStemmer s = new PorterStemmer();
String[] str = new String[]{"d://stop.txt"};
for (String key : str) {
InputStream in = new FileInputStream(key);
byte[] buffer = new byte[1024];
int bufferLen, offset, ch;
bufferLen = in.read(buffer);
offset = 0;
s.reset();
while (true) {
if (offset < bufferLen)
ch = buffer[offset++];
else {
bufferLen = in.read(buffer);
offset = 0;
if (bufferLen < 0)
ch = -1;
else
ch = buffer[offset++];
}
if (StringUtil.isLetter((char) ch)) {
s.add(Character.toLowerCase((char) ch));
} else {
s.stem();
System.out.print(s.toString());
s.reset();
if (ch < 0)
break;
else
System.out.print((char) ch);
}
}
in.close();
}
}
}