Question

I have a class Event that have two properties : “ID”, and “ExpirationTime”.
I have a list that have many events, some of them with the same ID.
I want to create an efficient LINQ query that will distinct the events by the ID, and for each ID keep the event with the smallest ExpirationTime.

Thanks!

Answer 1

The grouping is easy enough, but doing an efficient “MinBy” with standard LINQ to Objects is slightly messy:

var lowestByID = items.GroupBy(x => x.ID)
                      .Select(group => group.Aggregate((best, next) =>
                                   best.ExpirationTime < next.ExpirationTime 
                                  ? best : next));

It’s cleaner with a MinBy operator, such as the one provided with MoreLinq.

var lowestByID = items.GroupBy(x => x.ID)
                      .Select(group => group.MinBy(x => x.ExpirationTime));