try by creating a linq like in your comments just that this returns a list of arrays of string:
Here is the code:
(From row As DataRow In myDatatable Group row By id = row.Field(Of String)("ID") Into Group Select {id, String.Join(",", From i In Group Select i.Field(Of String)("Role"))}).ToList
If you need the result in a datatable you can build a new datatable
Make a for each of result and use the activity Add data row. In ArrayRow add the item and in DataTable the new data table
If you use the activity Output data table you can see the results