Hey guys - I'm stuck with this problem and im just wondering what the best way to handle it is.
Foreach (var customer in CustomerList)
{
Foreach (var appointment in AppointmentList)
{
if(appointment.customerId == customer.id)
customer.appointments.add(appointment)
}
}
this is the simplest way I can think to do it but im not sure if it's the most efficient!
Any help would be great-
Thanks.
You could perhaps pre-group the shorter list; this should give you better performance - I can't find citations to the exact big-O ratings since MSDN doesn't cite them, but it could be O(n + m) instead of O(n * m).
var apptsByCustomer = AppointmentList.ToLookup(appt => appt.customerId);
then you can use:
foreach (var customer in CustomerList) {
foreach(var appointment in apptsByCustomer[customer.id]) {
customer.appointments.add(appointment);
}
}
Or without LINQ (from comments):
// this bit is **broadly** comparable to ToLookup...
Dictionary<int, List<Appointment>> apptsByCustomer =
new Dictionary<int, List<Appointment>>();
List<Appointment> byCust;
foreach(Appointment appt in AppointmentList) {
if (!apptsByCustomer.TryGetValue(appt.customerId, out byCust)) {
byCust = new List<Appointment>();
apptsByCustomer.Add(appt.customerId, byCust);
}
byCust.Add(appt);
}
foreach (Customer cust in CustomerList) {
if (apptsByCustomer.TryGetValue(cust.id, out byCust)) {
foreach (Appointment appt in byCust) cust.appointments.Add(appt);
}
}
What about this?
foreach (var customer in CustomerList)
{
customer.AddRange( appointment.Where( a => a.CustomerId == customer.id));
}
For me this seems like a clear and concise syntax, and it explains what it does quite good.
Also, I think the performance should be fine here, and probably around the same as your original code.
You could use linq to remove nesting from loops, like this:
foreach (var customer in from customer in CustomerList
from appointment in AppointmentList
select customer)
{
// ...
}
You could make your customerList a Dictionary instead consisting of <id, cust>.
Then, instead of looping the list you try to get the value
Dictionary<int, Customer> customerList = new Dictionary<int, Customer>();
// populate your list
// ...
foreach (var appointment in AppointmentList)
{
Customer customer;
if (customerList.TryGetValue(appointment.customerID, out customer)){
// found the customer
customer.appointments.add(appointment)
}
This way, you let Dictionary optimize it for you.
Do note that if you only perform this action once, it's probably not worth optimizing much unless you see a notable slowdown from it. Premature optimization is not really worth the effort
