Hi John, I figured it out, ITariffDataImport is the interface my class implements and the string is one of three class properties that I possibly want to group by. I had to use parentheses instead of angle brackets after Func because of UT rendering limitations

Func(ITariffDataImport, string) grp = null;
                
                if (App.ImportSettings.RemoveDuplicates)
                {
                    Console.WriteLine("Removing duplicate tariffs...");
                    
                    if (App.tariffType == TariffType.BTInternational)
                        grp = s => s.Destination;
                    else
                        if (App.tariffType == TariffType.BTNational118)
                            grp = s => s.ChargeBand;
                        else
                            if (App.tariffType == TariffType.BTNationalIP)
                                grp = s => s.Service;

                    xlistint.Data = xlistint.Data.GroupBy(grp).Select(s => s.First()).ToList();

nice and clean I think.