Is it possible to do a Group By in LINQ but then only return the 'most recent' item (per group)?

Question

I'm trying to return the most recent item, per group, in .NET LINQ.

It reminds me of doing a PARTITION in Sql where we partition and get the top 1 per partition, ordered by most recent (per partition).

So far I've got the start of the linq code..

from p in products
group p by new {p.Provider.ProductId, p.Provider.Name} into g

But i'm not sure how to add the order by p.CreatedOn desc and just get the .Take(1), per partition/group.

Answer 1

Something like (appended at the end of your query):

select new {
    g.Key,
    Product = g.OrderByDescending(x => x.CreatedOn).First()
}

should do the job; or perhaps more conveniently:

select new {
    g.Key.ProductId,
    g.Key.Name,
    Product = g.OrderByDescending(x => x.CreatedOn).First()
}

Or if you don't need the key explicitly (because it is available under the item anyway), then just:

select g.OrderByDescending(x => x.CreatedOn).First()

Basically, each g is an IGrouping<T> (for some anonymous T), which means each g has a .Key property that is your group, and each g is an IEnumerable<> sequence of the original elements (presumably Product).