PorterStemmer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
    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/index.html

    Bug 1 (reported by Gonzalo Parra 16/10/99) fixed as marked below.
    Tthe words 'aed', 'eed', 'oed' leave k at 'a' for step 3, and b[k-1]
    is then out outside the bounds of b.

    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.

    [ This version is derived from Release 3, modified by Brian Goetz to
      optimize for fewer object creations.  ]

    Fetched and modified from https://svn.apache.org/repos/asf/opennlp/trunk/opennlp-tools/src/main/java/opennlp/tools/stemmer/PorterStemmer.java
*/

/**
 *
 * 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 {

    private char[] b;
    private int i, /* offset into b */
            j, k, k0;
    private boolean dirty = false;
    private static final int INC = 50;

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

    /**
     * reset() resets the stemmer so it can stem another word. If you invoke the
     * stemmer by calling add(char) and then stem(), you must call reset()
     * before starting another word.
     */
    public void reset() {
        i = 0;
        dirty = false;
    }

    /**
     * Add a character to the word being stemmed. When you are finished adding
     * characters, you can call stem(void) to process the word.
     */
    public void add(char ch) {
        if (b.length == i) {

            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.)
     */
    @Override
    public String toString() {
        return new String(b, 0, i);
    }

    /**
     * Returns the length of the word resulting from the stemming process.
     */
    public int getResultLength() {
        return i;
    }

    /**
     * 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 == k0) ? true : !cons(i - 1);
            default:
                return true;
        }
    }

    /* m() measures the number of consonant sequences between k0 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 = k0;
        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 <=> k0,...j contains a vowel */
    private final boolean vowelinstem() {
        int i;
        for (i = k0; 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 < k0 + 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 < k0 + 2 || !cons(i) || cons(i - 1) || !cons(i - 2)) {
            return false;
        } else {
            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 < k0) {
            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. */
    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;
        dirty = true;
    }

    /* r(s) is used further down. */
    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 = 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';
            dirty = true;
        }
    }

    /* 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 == k0) {
            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 <c>vcvc<v>. */
    private final void step5() {
        if (k == k0) {
            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 a word provided as a String. Returns the result as a String.
     */
    public String stem(String s) {
        if (stem(s.toCharArray(), s.length())) {
            return toString();
        } else {
            return s;
        }
    }

    /**
     * Stem a word provided as a CharSequence. Returns the result as a
     * CharSequence.
     */
    public CharSequence stem(CharSequence word) {
        return stem(word.toString());
    }

    /**
     * Stem a word contained in a char[]. 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 boolean stem(char[] word) {
        return stem(word, word.length);
    }

    /**
     * Stem a word contained in a portion of a char[] array. 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 boolean stem(char[] wordBuffer, int offset, int wordLen) {
        reset();
        if (b.length < wordLen) {
            b = new char[wordLen - offset];
        }
        System.arraycopy(wordBuffer, offset, b, 0, wordLen);
        i = wordLen;
        return stem(0);
    }

    /**
     * Stem a word contained in a leading portion of a char[] array. 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 boolean stem(char[] word, int wordLen) {
        return stem(word, 0, wordLen);
    }

    /**
     * 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 boolean stem() {
        return stem(0);
    }

    public boolean stem(int i0) {
        k = i - 1;
        k0 = i0;
        if (k > k0 + 1) {
            step1();
            step2();
            step3();
            step4();
            step5();
            step6();
        }
        // Also, a word is considered dirty if we lopped off letters
        // Thanks to Ifigenia Vairelles for pointing this out.
        if (i != k + 1) {
            dirty = true;
        }
        i = k + 1;
        return dirty;
    }
}