C # Data Grid View Cell Value

void Main()
{
    //Note: The following data is given here only to run the sameple code
    //in the actual program this data will be read from the DataBase
    DataTable teachers = new DataTable();
    teachers.Columns.Add("TeacherId",typeof(string),null);
    teachers.Columns.Add("TeacherName",typeof(string),null);
    teachers.Rows.Add("T1","Teacher1");
    teachers.Rows.Add("T2","Teacher2");
    
    DataTable classes = new DataTable();
    classes.Columns.Add("ClassId",typeof(string),null);
    classes.Columns.Add("TeacherId",typeof(string),null);
    classes.Rows.Add("C1","T1");
    classes.Rows.Add("C1","T2");
    classes.Rows.Add("C4","T1");
    classes.Rows.Add("C6","T2");
    classes.Rows.Add("C7","T1");
    classes.Rows.Add("C8","T1");
    //Note: The above data is given here only to run the sameple code
    //in the actual program this data will be read from the DataBase
    
    DataTable teacherClasses = new DataTable();
    teacherClasses.Columns.Add("TeacherId",typeof(string),null);
    teacherClasses.Columns.Add("Classes",typeof(string),null);
    DataTable teacherClasses2 = teacherClasses.Clone();
    	
    //Using LINQ
    teachers.AsEnumerable().Select (t => {
    	string teacherId = t.Field<string>("TeacherId");
    	string allClassIds = classes.AsEnumerable().Where (c => string.Equals(
            c.Field<string>("TeacherId"),teacherId, StringComparison.InvariantCulture))
            .Aggregate (string.Empty,(string allClasses, DataRow c) => 
                 allClasses + (string.IsNullOrEmpty(allClasses) ? string.Empty :
        	 ", ") + c.Field<string>("ClassId"));
        	teacherClasses.Rows.Add(teacherId,allClassIds);
    	return t;		
    }).Count();
    //Note: Count is called to execute the query, without this the query will not
    //be executed due to deferred execution model of LINQ.
    
    //Using DataTable Select method
    foreach(DataRow tRow in teachers.Rows){
    	string teacherId= tRow["TeacherId"].ToString();
    	DataRow[] allClassRows = classes.Select(
        	string.Format("TeacherId='{0}'",teacherId),
        	string.Empty);
    	string allClassIds = string.Empty;
    	foreach(DataRow row in allClassRows)
            allClassIds += (string.IsNullOrEmpty(allClassIds) ?
       		"" : ", ") + row["ClassId"].ToString();
    	teacherClasses2.Rows.Add(teacherId,allClassIds);
    }
}

//Contents of teacherClasses Table will be
//TeacherId Classes 
//T1 		C1, C4, C7, C8 
//T2 		C1, C6 </string></string></string>