DataSource Controls :: Ienumerable For Dropdown - Loop Through The Values Coming From Function?

Here is my code, using LinQ to get the data from database.

public IEnumerable categoryData()
{
db = new DBModelDataContext();
var cat = from c in db.Categories
select new { c.categoryname,c.categoryid };
return cat;
}

trying to get the values (categoryname and categoryid) into textfiled and valuefield of dropdown list.

dt = new clsData();
ddlCategory.DataSource = dt.categoryData();

what is the code that i need to write to assign the categoryname to textfield and categoryid to valuefield. I mean how to loop through the values coming from the above function.

ddlCategory.DataBind();