public void shift(int offset){
  for (int i=0; i < idxList.size(); i++) {
    idxList.set(i,idxList.get(i) + offset);
  }
}

public void shift ( int offset ) { for ( int i = 0 ; i < idxList . size ( ) ; i ++ ) { idxList . set ( i , idxList . get ( i ) + offset ) ; } }
shift the feature vector by offset
