public static Map<Integer, UrlDocLen> setupUrl(String url_file)
		{
			Map<Integer, UrlDocLen> url = new HashMap<Integer, UrlDocLen>();
			int length = 0;
			try {
				BufferedReader in = new BufferedReader(new FileReader(url_file));
				String line;
				while ((line = in.readLine()) != null) 
				{
					String words[] = line.split(" ");
					length += Integer.parseInt(words[2]);
					//insert into url
					url.put(Integer.parseInt(words[0]), new UrlDocLen(words[1],Integer.parseInt(words[2])));
				}
				//calculate the average length of documents in the collection
				avg_length = (double)length/url.size();
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
			return url;
		}