inside loop get ID No and check for Member column is blank or not if its not blank use store the member values in list or any dictionary. in dictionary you can use you ID as key and in value section use array and add you member values to that array.
note if Member column is blank then only create new item untill use same ID No untill you Member column is blank
string.join(",",(From row In dtInput.AsEnumerable() Group row By ID = row("ID NO").ToString() Into Group Let firstRow = Group.First() Let Members = String.Join(",", Group.Select(Function(r) r("Member").ToString()).Where(Function(s) Not String.IsNullOrWhiteSpace(s))) Select Members))
Premium
string.join(",",(From row In dtInput.AsEnumerable() Group row By ID = row("ID NO").ToString() Into Group Let firstRow = Group.First() Let Members = String.Join(",", Group.Select(Function(r) r("Premium").ToString()).Where(Function(s) Not String.IsNullOrWhiteSpace(s))) Select Members))
ok, let me explain,
so i have implemented this logic in a normal sequence
while, you are using RE Framework.
so you have to implement this logic in RE Framework