public static double purity(Vector<Tweet> t, String label) {
   double size = t.size();
   double tp = 0.0;
   for (Tweet tw : t) {
     if (tw.getLabel().equals(label)) {
       tp++;
     }
   }
   return tp / size;
 }
 public static double[] tp2(Vector<Tweet> t, String label, int actual) {
   double size = t.size();
   double[] tp = new double[3];
   for (Tweet tw : t) {
     if (tw.getLabel().equals(label)) {
       tp[0]++;
     }
   }
   tp[1] = tp[0] / t.size();
   tp[2] = tp[0] / actual;
   return tp;
 }