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DutchStemmer.javaAPI DocApache Lucene 2.1.010504Wed Feb 14 10:46:32 GMT 2007org.apache.lucene.analysis.nl

DutchStemmer

public class DutchStemmer extends Object
A stemmer for Dutch words. The algorithm is an implementation of the dutch stemming algorithm in Martin Porter's snowball project.
author
Edwin de Jonge (ejne at cbs.nl)

Fields Summary
private StringBuffer
sb
Buffer for the terms while stemming them.
private boolean
_removedE
private Map
_stemDict
private int
_R1
private int
_R2
Constructors Summary
Methods Summary
private booleanenEnding(java.lang.StringBuffer sb)

    String[] enend = new String[]{"ene", "en"};
    for (int i = 0; i < enend.length; i++) {
      String end = enend[i];
      String s = sb.toString();
      int index = s.length() - end.length();
      if (s.endsWith(end) &&
          index >= _R1 &&
          isValidEnEnding(sb, index - 1)
      ) {
        sb.delete(index, index + end.length());
        unDouble(sb, index);
        return true;
      }
    }
    return false;
private intgetRIndex(java.lang.StringBuffer sb, int start)

    if (start == 0)
      start = 1;
    int i = start;
    for (; i < sb.length(); i++) {
      //first non-vowel preceded by a vowel
      if (!isVowel(sb.charAt(i)) && isVowel(sb.charAt(i - 1))) {
        return i + 1;
      }
    }
    return i + 1;
private booleanisStemmable(java.lang.String term)
Checks if a term could be stemmed.

return
true if, and only if, the given term consists in letters.

    for (int c = 0; c < term.length(); c++) {
      if (!Character.isLetter(term.charAt(c))) return false;
    }
    return true;
private booleanisValidEnEnding(java.lang.StringBuffer sb, int index)

    char c = sb.charAt(index);
    if (isVowel(c))
      return false;
    if (c < 3)
      return false;
    // ends with "gem"?
    if (c == 'm" && sb.charAt(index - 2) == 'g" && sb.charAt(index - 1) == 'e")
      return false;
    return true;
private booleanisValidSEnding(java.lang.StringBuffer sb, int index)

    char c = sb.charAt(index);
    if (isVowel(c) || c == 'j")
      return false;
    return true;
private booleanisVowel(char c)

    switch (c) {
      case 'e":
      case 'a":
      case 'o":
      case 'i":
      case 'u":
      case 'y":
      case 'è":
        {
          return true;
        }
    }
    return false;
private voidreStoreYandI(java.lang.StringBuffer sb)

    String tmp = sb.toString();
    sb.delete(0, sb.length());
    sb.insert(0, tmp.replaceAll("I", "i").replaceAll("Y", "y"));
voidsetStemDictionary(java.util.Map dict)

    _stemDict = dict;
public java.lang.Stringstem(java.lang.String term)


  //TODO convert to internal
  /*
   * Stemms the given term to an unique <tt>discriminator</tt>.
   *
   * @param term The term that should be stemmed.
   * @return Discriminator for <tt>term</tt>
   */
      
    term = term.toLowerCase();
    if (!isStemmable(term))
      return term;
    if (_stemDict != null && _stemDict.containsKey(term))
      if (_stemDict.get(term) instanceof String)
        return (String) _stemDict.get(term);
      else
        return null;

    // Reset the StringBuffer.
    sb.delete(0, sb.length());
    sb.insert(0, term);
    // Stemming starts here...
    substitute(sb);
    storeYandI(sb);
    _R1 = getRIndex(sb, 0);
    _R1 = Math.max(3, _R1);
    step1(sb);
    step2(sb);
    _R2 = getRIndex(sb, _R1);
    step3a(sb);
    step3b(sb);
    step4(sb);
    reStoreYandI(sb);
    return sb.toString();
private voidstep1(java.lang.StringBuffer sb)

    if (_R1 >= sb.length())
      return;

    String s = sb.toString();
    int lengthR1 = sb.length() - _R1;
    int index;

    if (s.endsWith("heden")) {
      sb.replace(_R1, lengthR1 + _R1, sb.substring(_R1, lengthR1 + _R1).replaceAll("heden", "heid"));
      return;
    }

    if (enEnding(sb))
      return;

    if (s.endsWith("se") &&
        (index = s.length() - 2) >= _R1 &&
        isValidSEnding(sb, index - 1)
    ) {
      sb.delete(index, index + 2);
      return;
    }
    if (s.endsWith("s") &&
        (index = s.length() - 1) >= _R1 &&
        isValidSEnding(sb, index - 1)) {
      sb.delete(index, index + 1);
    }
private voidstep2(java.lang.StringBuffer sb)
Delete suffix e if in R1 and preceded by a non-vowel, and then undouble the ending

param
sb String being stemmed

    _removedE = false;
    if (_R1 >= sb.length())
      return;
    String s = sb.toString();
    int index = s.length() - 1;
    if (index >= _R1 &&
        s.endsWith("e") &&
        !isVowel(sb.charAt(index - 1))) {
      sb.delete(index, index + 1);
      unDouble(sb);
      _removedE = true;
    }
private voidstep3a(java.lang.StringBuffer sb)
Delete "heid"

param
sb String being stemmed

    if (_R2 >= sb.length())
      return;
    String s = sb.toString();
    int index = s.length() - 4;
    if (s.endsWith("heid") && index >= _R2 && sb.charAt(index - 1) != 'c") {
      sb.delete(index, index + 4); //remove heid
      enEnding(sb);
    }
private voidstep3b(java.lang.StringBuffer sb)

A d-suffix, or derivational suffix, enables a new word, often with a different grammatical category, or with a different sense, to be built from another word. Whether a d-suffix can be attached is discovered not from the rules of grammar, but by referring to a dictionary. So in English, ness can be added to certain adjectives to form corresponding nouns (littleness, kindness, foolishness ...) but not to all adjectives (not for example, to big, cruel, wise ...) d-suffixes can be used to change meaning, often in rather exotic ways.

Remove "ing", "end", "ig", "lijk", "baar" and "bar"

param
sb String being stemmed

    if (_R2 >= sb.length())
      return;
    String s = sb.toString();
    int index = 0;

    if ((s.endsWith("end") || s.endsWith("ing")) &&
        (index = s.length() - 3) >= _R2) {
      sb.delete(index, index + 3);
      if (sb.charAt(index - 2) == 'i" &&
          sb.charAt(index - 1) == 'g") {
        if (sb.charAt(index - 3) != 'e" & index - 2 >= _R2) {
          index -= 2;
          sb.delete(index, index + 2);
        }
      } else {
        unDouble(sb, index);
      }
      return;
    }
    if (s.endsWith("ig") &&
        (index = s.length() - 2) >= _R2
    ) {
      if (sb.charAt(index - 1) != 'e")
        sb.delete(index, index + 2);
      return;
    }
    if (s.endsWith("lijk") &&
        (index = s.length() - 4) >= _R2
    ) {
      sb.delete(index, index + 4);
      step2(sb);
      return;
    }
    if (s.endsWith("baar") &&
        (index = s.length() - 4) >= _R2
    ) {
      sb.delete(index, index + 4);
      return;
    }
    if (s.endsWith("bar") &&
        (index = s.length() - 3) >= _R2
    ) {
      if (_removedE)
        sb.delete(index, index + 3);
      return;
    }
private voidstep4(java.lang.StringBuffer sb)
undouble vowel If the words ends CVD, where C is a non-vowel, D is a non-vowel other than I, and V is double a, e, o or u, remove one of the vowels from V (for example, maan -> man, brood -> brod).

param
sb String being stemmed

    if (sb.length() < 4)
      return;
    String end = sb.substring(sb.length() - 4, sb.length());
    char c = end.charAt(0);
    char v1 = end.charAt(1);
    char v2 = end.charAt(2);
    char d = end.charAt(3);
    if (v1 == v2 &&
        d != 'I" &&
        v1 != 'i" &&
        isVowel(v1) &&
        !isVowel(d) &&
        !isVowel(c)) {
      sb.delete(sb.length() - 2, sb.length() - 1);
    }
private voidstoreYandI(java.lang.StringBuffer sb)

    if (sb.charAt(0) == 'y")
      sb.setCharAt(0, 'Y");

    int last = sb.length() - 1;

    for (int i = 1; i < last; i++) {
      switch (sb.charAt(i)) {
        case 'i":
          {
            if (isVowel(sb.charAt(i - 1)) &&
                isVowel(sb.charAt(i + 1))
            )
              sb.setCharAt(i, 'I");
            break;
          }
        case 'y":
          {
            if (isVowel(sb.charAt(i - 1)))
              sb.setCharAt(i, 'Y");
            break;
          }
      }
    }
    if (last > 0 && sb.charAt(last) == 'y" && isVowel(sb.charAt(last - 1)))
      sb.setCharAt(last, 'Y");
private voidsubstitute(java.lang.StringBuffer buffer)
Substitute ä, ë, ï, ö, ü, á , é, í, ó, ú

    for (int i = 0; i < buffer.length(); i++) {
      switch (buffer.charAt(i)) {
        case 'ä":
        case 'á":
          {
            buffer.setCharAt(i, 'a");
            break;
          }
        case 'ë":
        case 'é":
          {
            buffer.setCharAt(i, 'e");
            break;
          }
        case 'ü":
        case 'ú":
          {
            buffer.setCharAt(i, 'u");
            break;
          }
        case 'ï":
        case 'i":
          {
            buffer.setCharAt(i, 'i");
            break;
          }
        case 'ö":
        case 'ó":
          {
            buffer.setCharAt(i, 'o");
            break;
          }
      }
    }
private voidunDouble(java.lang.StringBuffer sb)

    unDouble(sb, sb.length());
private voidunDouble(java.lang.StringBuffer sb, int endIndex)

    String s = sb.substring(0, endIndex);
    if (s.endsWith("kk") || s.endsWith("tt") || s.endsWith("dd") || s.endsWith("nn") || s.endsWith("mm") || s.endsWith("ff")) {
      sb.delete(endIndex - 1, endIndex);
    }