In the current state of Dgraph, I don’t believe there is a way to do what you want.
Sets of strings can be used to filter nodes, but no logic to filter the sets themselves.
Furthermore, FYI from personal experience, regex function filters can become quite slow when you start working with a slightly large dataset. And there is also the restrictions that you cannot search for a regex if it is less than 3 characters long.
This might interest you: