CzechStemmer.java

package ivory.core.tokenize;

/**
 * @author Dolamic Ljiljana  University of Neuchatel
 *
 * Czech stemmer-removes case endings form nouns and adjetives, possesive adj.
 * endings from names
 * and takes care of palatalisation 
 */
public class CzechStemmer implements Stemmer {

  /**
   * A buffer of the current word being stemmed
   */
  private StringBuffer sb = new StringBuffer();


  /**
   * Default constructor
   */
  public CzechStemmer(){} // constructor

  public String stem(String input){

    //
    input=input.toLowerCase();

    //reset string buffer
    sb.delete(0,sb.length());
    sb.insert(0,input);

    // stemming...
    //removes case endings from nouns and adjectives
    removeCase(sb);

    //removes possesive endings from names -ov- and -in-
    removePossessives(sb);

    return sb.toString();
  }
  
  private void palatalise(StringBuffer buffer){
    int len=buffer.length();

    if( buffer.substring( len- 2 ,len).equals("ci")||
        buffer.substring( len- 2 ,len).equals("ce")||   
        buffer.substring( len- 2 ,len).equals("\u010di")||  //-či
        buffer.substring( len- 2 ,len).equals("\u010de")){  //-č 

      buffer.replace(len- 2 ,len, "k");
      return;
    }
    if( buffer.substring( len- 2 ,len).equals("zi")||
        buffer.substring( len- 2 ,len).equals("ze")||   
        buffer.substring( len- 2 ,len).equals("\u017ei")||  //-ži
        buffer.substring( len- 2 ,len).equals("\u017ee")){  //-že

      buffer.replace(len- 2 ,len, "h");
      return;
    }
    if( buffer.substring( len- 3 ,len).equals("\u010dt\u011b")||  //-čtě
        buffer.substring( len- 3 ,len).equals("\u010dti")||       //-čti  
        buffer.substring( len- 3 ,len).equals("\u010dt\u00ed")){  //-čté 

      buffer.replace(len- 3 ,len, "ck");
      return;
    }
    if( buffer.substring( len- 2 ,len).equals("\u0161t\u011b")||  //-ště
        buffer.substring( len- 2 ,len).equals("\u0161ti")||       //-šti
        buffer.substring( len- 2 ,len).equals("\u0161t\u00ed")){  //-šté

      buffer.replace(len- 2 ,len, "sk");
      return;
    }
    buffer.delete( len- 1 , len);
    return;
  }//palatalise

  private void removePossessives(StringBuffer buffer) {
    int len=buffer.length();

    if( len> 5 ){
      if( buffer.substring( len- 2 ,len).equals("ov")){

        buffer.delete( len- 2 , len);
        return;
      }
      if( buffer.substring( len-2,len).equals("\u016fv")){ //-ův

        buffer.delete( len- 2 , len);
        return;
      }
      if( buffer.substring( len- 2 ,len).equals("in")){

        buffer.delete( len- 1 , len);
        palatalise(buffer);
        return;
      }
    }
    return;
  }//removePossessives

  private void removeCase(StringBuffer buffer) {
    int len=buffer.length();
    // 
    if( (len> 7 )&&
        buffer.substring( len- 5 ,len).equals("atech")){

      buffer.delete( len- 5 , len);
      return;
    }//len>7
    if( len> 6 ){
      if(buffer.substring( len- 4 ,len).equals("\u011btem")){ //-ětem

        buffer.delete( len- 3 , len);
        palatalise(buffer);
        return;
      }
      if(buffer.substring( len- 4 ,len).equals("at\u016fm")){  //-atům
        buffer.delete( len- 4 , len);
        return;
      }

    }
    if( len> 5 ){
      if(buffer.substring( len-3,len).equals("ech")|| 
          buffer.substring( len-3,len).equals("ich")|| 
          buffer.substring( len-3,len).equals("\u00edch")){ //-ích

        buffer.delete( len-2 , len);
        palatalise(buffer);
        return;
      }
      if(buffer.substring( len-3,len).equals("\u00e9ho")|| //-ého
          buffer.substring( len-3,len).equals("\u011bmi")||  //-ěmi
          buffer.substring( len-3,len).equals("emi")||
          buffer.substring( len-3,len).equals("\u00e9mu")||  //ému
          buffer.substring( len-3,len).equals("\u011bte")||  //-ěte
          buffer.substring( len-3,len).equals("\u011bti")||  //-ěti
          buffer.substring( len-3,len).equals("iho")||
          buffer.substring( len-3,len).equals("\u00edho")||  //-ího
          buffer.substring( len-3,len).equals("\u00edmi")||  //-ími
          buffer.substring( len-3,len).equals("imu")){

        buffer.delete( len- 2 , len);
        palatalise(buffer);
        return;
      }
      if( buffer.substring( len-3,len).equals("\u00e1ch")|| //-ách
          buffer.substring( len-3,len).equals("ata")||
          buffer.substring( len-3,len).equals("aty")||
          buffer.substring( len-3,len).equals("\u00fdch")||   //-ých
          buffer.substring( len-3,len).equals("ama")||
          buffer.substring( len-3,len).equals("ami")||
          buffer.substring( len-3,len).equals("ov\u00e9")||   //-ové
          buffer.substring( len-3,len).equals("ovi")||
          buffer.substring( len-3,len).equals("\u00fdmi")){  //-ými

        buffer.delete( len- 3 , len);
        return;
      }
    }  
    if( len> 4){
      if(buffer.substring( len-2,len).equals("em")){

        buffer.delete( len- 1 , len);
        palatalise(buffer);
        return;

      }
      if( buffer.substring( len-2,len).equals("es")|| 
          buffer.substring( len-2,len).equals("\u00e9m")||    //-ém
          buffer.substring( len-2,len).equals("\u00edm")){   //-ím

        buffer.delete( len- 2 , len);
        palatalise(buffer);
        return;
      }
      if( buffer.substring( len-2,len).equals("\u016fm")){  //-ům

        buffer.delete( len- 2 , len);
        return;

      }
      if( buffer.substring( len-2,len).equals("at")|| 
          buffer.substring( len-2,len).equals("\u00e1m")||    //-ám
          buffer.substring( len-2,len).equals("os")||
          buffer.substring( len-2,len).equals("us")||   
          buffer.substring( len-2,len).equals("\u00fdm")||     //-ým
          buffer.substring( len-2,len).equals("mi")||   
          buffer.substring( len-2,len).equals("ou")){

        buffer.delete( len- 2 , len);
        return;
      }
    }//len>4
    if( len> 3){
      if( buffer.substring( len-1,len).equals("e")||
          buffer.substring( len-1,len).equals("i")){

        palatalise(buffer);
        return;

      }
      if( buffer.substring( len-1,len).equals("\u00ed")||  //-í
          buffer.substring( len-1,len).equals("\u011b")){ //-ě

        palatalise(buffer);
        return;
      }
      if( buffer.substring( len-1,len).equals("u")||
          buffer.substring( len-1,len).equals("y")||
          buffer.substring( len-1,len).equals("\u016f")){  //-ů

        buffer.delete( len- 1 , len);
        return;

      }
      if( buffer.substring( len-1,len).equals("a")||
          buffer.substring( len-1,len).equals("o")||
          buffer.substring( len-1,len).equals("\u00e1")||  // -á
          buffer.substring( len-1,len).equals("\u00e9")||  //-é
          buffer.substring( len-1,len).equals("\u00fd")){   //-ý

        buffer.delete( len- 1 , len);
        return;
      }
    }//len>3
  }

  @Override
  public String toStem(String token) {
    return stem(token);
  }
  
}//CzechStemmer_1