LINQ groupby question

Question

I have a collection called navigationList. This list holds customer objects. A customer has a property called Town.

The list holds 5 customers: 2 with town "New York", and 5 with town "Madrid".

I want the list to only hold only 2 customers. 1 with town "New York" and one with "Madrid". If 2 are from "New York", I want the last one. Same for "Madrid".

What would the LINQ statement look like?

var newList = navigationList.GroupBy(c => c.Town) // ? 

Answer 1

You would want something like

var newList = navigationList.GroupBy(c => c.Town).Select(g => g.Last()).ToList();

However, you would probably want to OrderBy first, so that the Last is meaningful:

var newList = navigationList.
              GroupBy(c => c.Town).
              Select(g => g.OrderBy(c => c.Id).Last()).
              ToList();

In this case the ordering is done by customer Id.