linq group by with c#
public IQueryable result(string username, string exam)
     {

        return (from result in idb.User_Exam_Question
                where (result.User_Tbl_email == username && result.Exam_Tbl_ID ==   Convert.ToInt32(exam))
                group result by result.category_tbl_ID into cat
                select cat);
    }

public int result(string username, string exam)
{
    return (from result in idb.User_Exam_Question
            where (result.User_Tbl_email == username && result.Exam_Tbl_ID == Convert.ToInt32(exam))
            group result by result.category_tbl_ID into cat
            select cat).Count();
}

public IQueryable result(string username, string exam)
{
    return from result in idb.User_Exam_Question
           where (result.User_Tbl_email == username && result.Exam_Tbl_ID == Convert.ToInt32(exam))
           group result by result.category_tbl_ID into cat
           select new
           {
               CatCount = cat.Count()
           }
}

result("username", "exam")[0].CatCount;
// returns the count of the first result of the query.

public IQueryable result(string username, string exam)
     {

        return (from result in idb.User_Exam_Question
                where (result.User_Tbl_email == username && result.Exam_Tbl_ID ==   Convert.ToInt32(exam))
                group result by result.category_tbl_ID into cat
                select new { Group = cat , Count = cat.Count()  } );
    }