/**
  * Metoda zwraca œrednia liczbê zebranch ankiet na dzieñ przez wybranego ankietera, licz¹ siê
  * tylko te dni, wktórych pracowa³.
  *
  * @param surveys
  * @param interviewer
  * @param from
  * @param to
  * @return
  */
 public float getMeanFilledSurveysOnADay(
     List<Survey> surveys, Interviewer interviewer, GregorianCalendar from, GregorianCalendar to) {
   float mean;
   float days = numberOfDaysInWork(interviewer, from, to);
   long numberOfSurveys = 0;
   for (Survey survey : surveys) {
     if (survey.getFinishTime().compareTo(from) >= 0
         && survey.getFinishTime().compareTo(to) <= 0) {
       numberOfSurveys += 1;
     }
   }
   mean = numberOfSurveys / days;
   return mean;
 }
 /**
  * Metoda zwraca liczbê wype³nionych ankiet.
  *
  * @param surveys
  * @return
  */
 public int getAmountOfFilledSurveys(List<Survey> surveys) {
   int amount = 0;
   if (surveys != null) {
     for (Survey survey : surveys) {
       if (survey.getFinishTime() != null) {
         amount += 1;
       }
     }
     return amount;
   } else {
     return 0;
   }
 }
 /**
  * Metoda zwraca œredni¹ liczbê zebranych ankiet przez ankietera na dzieñ w ci¹gu okresu, wktórym
  * pracowa³
  *
  * @param surveys
  * @param interviewer
  * @return
  */
 public float getMeanFilledSurveysOnADay(List<Survey> surveys, Interviewer interviewer) {
   float mean;
   float days = numberOfDaysInWork(interviewer);
   long numberOfSurveys = 0;
   if (surveys != null) {
     for (Survey survey : surveys) {
       if (survey.getFinishTime() != null) {
         numberOfSurveys += 1;
       }
     }
     mean = numberOfSurveys / days;
     return mean;
   } else {
     return 0;
   }
 }
 /**
  * Metoda zwraca mapê, która zawiera jako klucze poszczególne dni w których ankieter zebra³ jakieœ
  * ankiety, zaœ wartoœciami s¹ liczby zebranych ankiet w tym dniu.
  *
  * @param surveys
  * @param interviewer
  * @return
  */
 public HashMap<GregorianCalendar, Integer> getAmountOfFilledSurveysInDays(
     List<Survey> surveys, Interviewer interviewer) {
   HashMap<GregorianCalendar, Integer> filledSurveysInDays =
       new HashMap<GregorianCalendar, Integer>();
   for (Survey survey : surveys) {
     GregorianCalendar data = survey.getFinishTime();
     int year = data.get(Calendar.YEAR);
     int month = data.get(Calendar.MONTH);
     int day = data.get(Calendar.DAY_OF_MONTH);
     GregorianCalendar date = new GregorianCalendar(year, month, day);
     if (!filledSurveysInDays.containsKey(date)) {
       filledSurveysInDays.put(date, 1);
     } else {
       filledSurveysInDays.put(date, filledSurveysInDays.get(date) + 1);
     }
   }
   return filledSurveysInDays;
 }