unstableSortBy +containers

unstableSortBy :: (a -> a -> Ordering) -> Seq a -> Seq a
containers Data.Sequence
O(n log n). A generalization of unstableSort, unstableSortBy takes an arbitrary comparator and sorts the specified sequence. The sort is not stable. This algorithm is frequently faster and uses less memory than sortBy, and performs extremely well -- frequently twice as fast as sortBy -- when the sequence is already nearly sorted.