LINQ Using Max() to select a single row

Question

I\'m using LINQ on an IQueryable returned from NHibernate and I need to select the row with the maximum value(s) in a couple of fields.

I\'ve simplified the bit tha

Answer 1

Addressing the first question, if you need to take several rows grouped by certain criteria with the other column with max value you can do something like this:

var query =
    from u1 in table
    join u2 in (
        from u in table
        group u by u.GroupId into g
        select new { GroupId = g.Key, MaxStatus = g.Max(x => x.Status) }
    ) on new { u1.GroupId, u1.Status } equals new { u2.GroupId, Status = u2.MaxStatus}
    select u1;

Answer 2

Simply in one line:

var result = table.First(x => x.Status == table.Max(y => y.Status));

Notice that there are two action. the inner action is for finding the max value, the outer action is for get the desired object.

Answer 3

I don't see why you are grouping here.

Try this:

var maxValue = table.Max(x => x.Status)
var result = table.First(x => x.Status == maxValue);

An alternate approach that would iterate table only once would be this:

var result = table.OrderByDescending(x => x.Status).First();

This is helpful if table is an IEnumerable<T> that is not present in memory or that is calculated on the fly.

Answer 4

You can group by status and select a row from the largest group:

table.GroupBy(r => r.Status).OrderByDescending(g => g.Key).First().First();

The first First() gets the first group (the set of rows with the largest status); the second First() gets the first row in that group.
If the status is always unqiue, you can replace the second First() with Single().

Answer 5

You can also do:

(from u in table
orderby u.Status descending
select u).Take(1);

Answer 6

More one example:

Follow:

 qryAux = (from q in qryAux where
            q.OrdSeq == (from pp in Sessao.Query<NameTable>() where pp.FieldPk
            == q.FieldPk select pp.OrdSeq).Max() select q);

Equals:

 select t.*   from nametable t  where t.OrdSeq =
        (select max(t2.OrdSeq) from nametable t2 where t2.FieldPk= t.FieldPk)