org.tartarus.snowball.ext.porterStemmerOriginal Maven / Gradle / Ivy
/*
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
*/
package org.tartarus.snowball.ext;
//import java.io.*;
/**
* 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 porterStemmerOriginal
{
private static class porterStemmerAlgo
{
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 porterStemmerAlgo()
// { 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,
gives 0
vc gives 1
vcvc gives 2
vcvcvc 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 vcvc. */
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;
}
public String getStem(String word)
{ i = word.length();
b = word.toCharArray();
stem();
return new String(b, 0, i_end);
}
} // porterStemmerAlgo
/** 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)
// { System.out.println(porterStemmerOriginal.getStem("communications"));
// System.out.println(porterStemmerOriginal.getStem("friendships"));
// System.out.println(porterStemmerOriginal.getStem("cannon"));
// }
public static String getStem(String word)
{ return new porterStemmerAlgo().getStem(word);
}
} // porterStemmerOriginal
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