That's not entirely stupid, one could certainly do that under some circumstances. E.g. when sorting by one key and looking up via another, one could create a form of partial index in an array, and perform lookups in parallel. (As per the OrderSort algorithm by Matthew Aitkenhead and Mark Richards - 2005)
However, generally if modifying the data structure was an option, I would change it entirely, and what I chose would probably not have anything that would benefit from threading.