How can one create custom index column by group for a data dynamically received from the web.|Power Query|Excel Forum|My Online Training Hub

Good day forum members, pls i am stuck at creating a custom index column for a data that has a subgroup.

The data is received online and i what to dynamically create unique identity number based on the class columns.

Note: the class column is receiving the class  field one after the other, as the report is been sent.So that any record that comes in look into the class column field or values and generate  auto incremented ID based  on the class ....Classes are :LM1, FDI,UB1. Sorting of any data columns shouldnt change the pattern.

I have been cogitating on this.

Please, see my attached file.The table by  left, shows the challenge, while the one on the right shows an expected results.

Thank you.