public void SetDoctors(List <ClinicAppointment> appointmentList) { if (appointmentList == null) { return; } Doctor[] doctorsArr = new Doctor[MaxDoctors]; int index = 0; foreach (ClinicAppointment appt in appointmentList) { if (index >= MaxDoctors) { break; } if (!doctorsArr.Contains(appt.Doctor, new DoctorComparer())) { doctorsArr[index] = appt.Doctor; index++; } } Doctors = new ObservableCollection <Doctor>(doctorsArr); }