For 1, it wouldn’t change because you’re accessing the same data type, all the fields are the same.
For 2, Parent group’s thing is the group outside of the repeating group, it would be of no use even if I use a state because you would only be able to use one element still and not the current cell you are accessing.
Because I’m trying to sort it with an attribute that is derived (you use a formula for it and not store it in the database) rather than stored, I think it isn’t possible. However, I was able to do it by creating a new entity called ‘Past Order’ that contained the ‘Product’ and a number ‘Quantity’, and update this accordingly.
This was also the solution of other people trying to sort a user based on their follower count. You normally only need the followers attribute. But in order to sort the users based on the count, you would have to add the followers_count attribute and update it each time another user adds to the followers. Here: Sorting a Repeating Group by Users in List - #3 by NigelG