LINQ partition by

static void Main (string[] args)
        {
            var beatles = (new[] {new {id=1, Inst = "Guitar", Name= "John"},
new {i  d=2, inst = "Guitar", Name= "George"},
new {id=3, Inst = "Guitar", Name= "Paul"},
new {id=4, Inst = "Drums" , name= "Ringo"},
new {id=5, Inst = "Drums", Name= "Pete"}
);

            Method 1
            //Method 2

            foreach (var i in O)
            {
                Console.WriteLine ("{0} {1} {2}", I.inst, I.name, i.rn);
            }

            Console.ReadLine ();
        }

Method 1:

var o = Beatles. By (M => m.id). ToList (). GroupBy (x => x.inst)
                . SelectMany (t => t.select ((b, i) => new {b, i})). Select (M => m.b);

Method 2:

var o = Beatles. By (x => x.id). GroupBy (x => x.inst)
            . Select (g => new {g, Count = G.count ()})
            . SelectMany (t => t.g.select (b => b). Zip (Enumerable.range (1, T.count), (J, i) => new {j.inst, j.name, RN = i}));

Results:

Guitar John 1 
guitar George 2 
guitar Paul 3 
drums Ringo 1