How to set a property in a collection based on the join?

[sri_3464 0]

i have two collections defined below

List lstScienceStudents = GetScienceStudentCollection();
List lstMathsStudents = GetMathsStudentCollection();

Now both the classes ScienceStudents and MathsStudents have a common id Student_Id. I need to set the boolean property IsMathStudent in lstScienceStudents to true by joining the two collection. To be more clear here is the code

for (int i = 0; i < lstScienceStudents .Count; i++)
{
for (int j = 0; j < lstMathsStudents.Count; j++)
{
if (lstScienceStudents[i].Student_Id == lstMathsStudents[j].Student_Id)
lstScienceStudents[i].IsMathStudent = true;
}
}

I know i can get the collection of MathsStudents in ScienceStudent collection using join in linq. But i need to set the flag to true in the lstScienceStudent collection list. How can i do it?

[Dan Mos]

You can't modify a field during a Linq query. But, you can return a new IEnuerable(T) or List(T) Something like this:

  var needed = from sRec in lstScienceStudents
         from mRec in lstMathsStudents
         where sRec.Student\_Id.Equals(mRec.Student\_Id)
         select new{
             Field1here = YouKnowWhat;
             Field2here = YouKnowWhat;
         }