PorterStemmer.java

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.
 */

class PorterStemmer
{
  private char[] b;
  private int i,    /* offset into b */
    j, k, k0;
  private boolean dirty = false;
  private static final int INC = 50; /* unit of size whereby b is increased */
  private static final int EXTRA = 1;

  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 + EXTRA) {
      char[] new_b = new char[b.length+INC];
      System.arraycopy(b, 0, new_b, 0, b.length);
      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 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) {
      char[] new_b = new char[wordLen + EXTRA];
      b = new_b;
    }
    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;
  }

  /** Test program for demonstrating the Stemmer.  It reads a file and
   * stems each word, writing the result to standard out.
   * Usage: Stemmer file-name
   */
  public static void main(String[] args) {
    PorterStemmer s = new PorterStemmer();

    for (int i = 0; i < args.length; i++) {
      try {
        InputStream in = new FileInputStream(args[i]);
        byte[] buffer = new byte[1024];
        int bufferLen, offset, ch;

        bufferLen = in.read(buffer);
        offset = 0;
        s.reset();

        while(true) {
          if (offset < bufferLen)
            ch = buffer[offset++];
          else {
            bufferLen = in.read(buffer);
            offset = 0;
            if (bufferLen < 0)
              ch = -1;
            else
              ch = buffer[offset++];
          }

          if (Character.isLetter((char) ch)) {
            s.add(Character.toLowerCase((char) ch));
          }
          else {
             s.stem();
             System.out.print(s.toString());
             s.reset();
             if (ch < 0)
               break;
             else {
               System.out.print((char) ch);
             }
           }
        }

        in.close();
      }
      catch (IOException e) {
        System.out.println("error reading " + args[i]);
      }
    }
  }
}