reaction formation: U do the exact opposite of what u think or feel.
If u hate someone but u give them a flower, that's reaction formation.
Sublimation: U do the same as u feel but in a good way instead of a bad way.
Jack the ripper becomes a surgeon. U like the smell of blood, u become a surgeon instead of a serial killer but u still cut ppl up.
Sorry I don't remember any clinical examples but just keep these rules in ur head.
My understanding is that sublimation is channeling unacceptable drives/emotions into socially acceptable actions (eg, want to kick a puppy but instead enroll in a karate club).
Reaction formation, on the other hand, is characterised by denying/avoiding the unacceptable drive/emotion and parading a directly opposite attitude (eg, want to kick a puppy and become an animal rights activist ).
Sublimation is mature; reaction formation is an immature defence mechanism (so, you cannot really say that reaction formation is subset of sublimation).
I am sure there is a better explanation, but I can't think of one right now.