How to match data between 3 columns

when readin int the excel into a datatable (read range) we would expect following result


so we would

  • filling up the missing GroupX column values
  • grouping the data on GroupDocs
  • processing / evaluating the groups

For filling up, have a starter help here:
FillUp_BlockBlanks.xaml (9.3 KB)

Grouping data have alook here: