stemmer.java

一个很不错的词频统计程序,目前只支持英文,中文的本人正在修改中.改好后上传给大家分享

package edu.udo.cs.wvtool.external;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

/**
 * 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 Stemmer {
    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 Stemmer() {
        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,
     * 
     * <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':
            if (ends("enci")) {
                r("ence");
                break;
            }
            if (ends("anci")) {
                r("ance");
                break;
            }
            break;
        case 'e':
            if (ends("izer")) {
                r("ize");
                break;
            }