porterstemmer.java

wekaUT是 university texas austin 开发的基于weka的半指导学习(semi supervised learning)的分类器

package weka.datagenerators;

import java.util.ArrayList;
import java.util.Collection;

/**
 * Finds the lexeme of a given inflected form by stripping off suffixes.
 * This stemmer only works for English.
 *
 * <p>This filter has no parameters.
 *
 * <p>The Porter stemming algorithm is documented in: Porter, M.F.,
 * <i>"An Algorithm For Suffix Stripping,"</i> Program 14 (3), July 1980,
 * pp. 130-137.
 *
 * <p>This code is an adaptation of the Java code that appears in
 * <code>http://www.tartarus.org/~martin/PorterStemmer</code>.  The
 * stemming function converts its input to lowercase.
 *
 * <p>Original author: Martin Porter
 *
 * <p><b>History:</b>
 *
 * <p><i>Release 1</i>
 *
 * <p>Bug 1 (reported by Gonzalo Parra 16/10/99) fixed as marked below.
 * The words <code>'aed'</code>, <code>'eed'</code>, <code>'oed'</code>
 * leave <code>k</code> at <code>'a'</code> for step 3, and
 * <code>b[k-1]</code> is then out outside the bounds of <code>b</code>.
 *
 * <p><i>Release 2</i>
 *
 * <p>Similarly, bug 2 (reported by Steve Dyrdahl 22/2/00) fixed as
 * marked below.  <code>'ion'</code> by itself leaves <code>j = -1</code>
 * in the test for <code>'ion'</code> in step 5, and <code>b[j]</code> is
 * then outside the bounds of <code>b</code>.
 *
 * <p><i>Release 3</i>
 *
 * <p>Considerably revised 4/9/00 in the light of many helpful
 * suggestions from Brian Goetz of Quiotix Corporation
 * (<code>[e-mail]</code>).
 *
 * <p><i>Release 4</i>
 *
 * @author ywwong
 * @version $Id: PorterStemmer.java,v 1.1.1.1 2003/01/22 07:48:27 mbilenko Exp $
 */

class PorterStemmer implements TokenFilter {

    /** Unit of size whereby the character buffer is increased. */
    private static final int INC = 50;

    /** The character buffer. */
    private char[] b;

    /** Offset into the character buffer. */
    private int i;

    /** Offset to end of stemmed word. */
    private int i_end;

    private int j;
    private int k;

    /** Creates a Porter stemmer filter.
     *
     * @param ts  The TextSource object.
     */
    public PorterStemmer(TextSource ts, String[] options) throws Exception {
        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.
     */
    protected 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.)
     */
    protected String getString() { return new String(b,0,i_end); }

    /** cons(i) is true iff 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 iff 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 iff 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 iff 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) {
        int ch;

        if (i < 2 || !cons(i) || cons(i-1) || !cons(i-2))
            return false;
        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)) {
                int ch;

                k--;
                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() {
        // For Bug 1
        if (k == 0)
            return;
        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() {
        // for Bug 1
        if (k == 0)
            return;
        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;
            // element etc. not stripped before the m
            if (ends("ment"))
                break;
            if (ends("ent"))
                break;
            return;
        case 'o':
            // j >= 0 fixes Bug 2
            if (ends("ion") && j >= 0 && (b[j] == 's' || b[j] == 't'))
                break;
            // takes care of -ous
            if (ends("ou"))
                break;
            return;
        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().  You can retrieve the result with getString().
     */
    protected void stem() {
        k = i - 1;
        if (k > 1) {
            step1();
            step2();
            step3();
            step4();
            step5();
            step6();
        }
        i_end = k+1; i = 0;
    }

    /** Applies the Porter Stemmer.
     *
     * @param strToken  The input token.
     * @return The root of the input token.
     */
    public String apply(String strToken) {
        int nLen;
        char c;

        // Check to ensure the word is all alphabetic.
        nLen = strToken.length();
        for (int j = 0; j < nLen; ++j) {
            c = strToken.charAt(j);
            if (Character.isLetter(c))
                add(Character.toLowerCase(c));
            else {
                i = 0;
                return strToken;
            }
        }

        stem();
        return getString();
    }

    /* This is for debugging. */
    public static void main(String[] args) throws Exception {
        TokenFilter st = new PorterStemmer(null, null);
        String str;

        for (int i = 0; i < args.length; ++i) {
            str = st.apply(args[i]);
            if (str != null)
                System.out.println(str);
        }
    }

    ////// WEKA specific. //////

    public static Collection listOptions() {
        return new ArrayList();
    }

    public Collection getOptions() {
        return new ArrayList();
    }

}