public HashMap<String, Double> getVector(){
		if(vector != null)
			return vector;
		
		if(subclasses.size() == 0)
			return null;
		
		HashMap<String, Double> combined = new HashMap<String, Double>();
		for(TrainedQuestionClass t : subclasses){
			HashMap<String, Double> sub = t.getVector();
			for(String s : sub.keySet()){
				if(!combined.containsKey(s))
					combined.put(s, 0.0);
				combined.put(s, combined.get(s) + sub.get(s));
			}
		}
		vector = combined;
		return combined;
	}