How do I select variable fields in a LINQ Select statement?

[Christhemist]

The fields in which will be selected will change each time. Also, I am selecting from several lists so it makes it hard to use a string list.

Here is my code: (Note: This works manually but once the field names change it will not work.)

Dim both = From row1 In AddressListDatatable.AsEnumerable()
                   Join row2 In Matrix1Datatable.AsEnumerable()
                   On row1.Field(Of String)("Offercode") Equals row2.Field(Of String)("Code")
                   Select row1("Account") & "," & row1("First") & "," & row2("CODE") & "," & row2("SWITCH") 

As you can see I am selecting different fields from two DataTables. However, the name and quantity of these fields will change often. I came up with the following solution but it won't work with multiple lists. (Note: I already populated the string list "ListOfColumnNames" prior to running this code)

Here is that code:

Dim both = From row1 In AddressListDatatable.AsEnumerable()
                   Join row2 In Matrix1Datatable.AsEnumerable()
                   On row1.Field(Of String)("Offercode") Equals row2.Field(Of String)("Code")
                   Select String.Join(", ", From i In ListOfColumnNames Select row1(i))