protected override IEnumerable <IRow> MutateRow(IRow row) { foreach (var column in ColumnsToMerge) { if (_sb.Length > 0) { _sb.Append(Separator); } var value = row.GetAs <string>(column, null); if (!string.IsNullOrEmpty(value)) { _sb.Append(value); } row.SetStagedValue(column, null); } row.SetStagedValue(TargetColumn, _sb.ToString()); _sb.Clear(); row.ApplyStaging(); yield return(row); }