porterstemmer.java

dragontoolkit用于机器学习

package dragon.nlp.tool;

import java.io.*;
/**
 * <p>Porter stemmer</p>
 * <p> </p>
 * <p>Copyright: Copyright (c) 2005</p>
 * <p>Company: IST, Drexel University</p>
 * @author Davis Zhou
 * @version 1.0
 */

public class PorterStemmer implements Lemmatiser{
    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 PorterStemmer() {
        b = new char[INC];
        i = 0;
        i_end = 0;
    }

    /*added by davis*/
    public String stem(String word){

        for(int i=0;i<word.length();i++)
            add(word.charAt(i));
        stem();
        return toString();
    }

    public String lemmatize(String word){
        return stem(word);
    }

    public String lemmatize(String word, int POS){
        return stem(word);
    }
    //ended

    /**
     * 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,
          <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 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':