var list = new[] { 
   new { id=1, name="a" },
   new { id=1, name="a" },
   new { id=2, name="b" },
   new { id=3, name="c" },
   new { id=3, name="c" },
   new { id=2, name="b" },
   new { id=2, name="b" },
};

var result = list.GroupBy(x => x.id).Select(g => new { id = g.Key, count = g.Count(), name = g.First(s => s.id == g.Key).name });
foreach (var r in result)
    Console.WriteLine("id:{0} name:{1} count:{2}", r.id, r.name, r.count);

------解决方案--------------------
取group的第一个元素.

C# code
var result = list.GroupBy(x => x.id).Select(g => new { id = g.Key, count = g.Count(), item = g.First() });
foreach (var r in result)
    Console.WriteLine("id:{0} name:{1} count:{2}", r.id, r.item.name, r.count);

------解决方案--------------------
C# code
    public class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }
    protected void Page_Load(object sender, EventArgs e)
    {
        List<Student> studentList = new List<Student>();
        studentList.Add(new Student { Id = 1, Name = "1" });
        studentList.Add(new Student { Id = 2, Name = "2" });
        studentList.Add(new Student { Id = 2, Name = "3" });
        studentList.Add(new Student { Id = 3, Name = "4" });
        studentList.Add(new Student { Id = 3, Name = "5" });
        studentList.Add(new Student { Id = 3, Name = "6" });
        studentList.Add(new Student { Id = 4, Name = "7" });
        studentList.Add(new Student { Id = 5, Name = "8" });
        studentList.Add(new Student { Id = 6, Name = "9" });
        studentList.Add(new Student { Id = 7, Name = "10" });
        var results = studentList.Select(o => new
        {
            Id = o.Id,
            Name = o.Name,
            Count = studentList.Where(s => s.Id == o.Id).Count()
        });

        foreach (var item in results)
        {
            Response.Write(string.Format("Id={0},Name={1},Count={2}", item.Id, item.Name, item.Count));
            Response.Write("<br/>");
        }
    }