package edu.northwestern.at.utils.corpuslinguistics.stemmer;
/* Please see the license information in the header below. */
/*
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 (brian@quiotix.com).
Release 4
*/
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 PorterStemmer implements Stemmer
{
protected char[] b;
protected int i, /* offset into b */
i_end, /* offset to end of stemmed word */
j, k;
protected static final int INC = 50;
/* unit of size whereby b is increased */
public PorterStemmer()
{
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. */
protected 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
....
*/
protected 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 */
protected 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. */
protected 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.
*/
protected 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;
}
protected 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. */
protected 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. */
protected 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
*/
protected 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. */
protected 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. */
protected 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. */
protected 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>. */
protected 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. */
protected 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 stem( String word )
{
i = 0;
i_end = 0;
for ( int j = 0 ; j < word.length() ; j++ )
{
add( word.charAt( j ) );
}
stem();
return toString();
}
}