Quick summary (I can provide a more exhaustive explanation if there is interest and when I have bit more time available):
In addition to the main RG on the page, I have a second hidden RG.
The main RG has the primary data type for its source, while the hidden RG has the related type.
Within the first plugin is the “RG Extractor”. I use this to get the related data out of the hidden RG.
Within the second plugin is “Transform Lists”. I use this to stipulate the sort order.
Then in my main visible RG, there is a condition (actually multiple) to activate the related sorting based on user selection. Took a little while to get working, but thanks to some wonderful support from @gaurav it works perfectly and super quick too.
But just to confirm before I dive into this, this setup will also work to sort calculated values (values not stored in the database) inside of the primary repeating group??
Sorry, I really don’t know the answer to this. I’m not that optimistic, because the solution relies on the RG extractor which gets existing data already in the related type.