public static HashMap<Double,Integer>statistics(ArrayList<ArrayList<Double>>D){
	    HashMap<Double,Integer>statisticsMap=new HashMap<Double,Integer>();
	    if(D.size()==0){
	    	return statisticsMap;
	    }
	    int attribte_list_size=D.get(0).size()-1;
		try{
			for(int i=0;i<D.size();i++){
				Double classify=D.get(i).get(attribte_list_size);//提取出元组类别
				if(statisticsMap.containsKey(classify)){
					statisticsMap.put(classify, statisticsMap.get(classify)+1);
				}
				else{
					statisticsMap.put(classify, 1);
				}
			}
		}catch(Exception e){
			e.printStackTrace();
		}
		return statisticsMap;
	}