[Feature request] slice a sorted dataframe
Say I have a dataframe `df` with two columns `guest_name`, `room_nr` and I want the room numbers of a specific guest, we can slice that `df.loc[df["guest_name"]==guest],"room_nr"]`. 
I have (to be honest) not looked into how the slicing is done as such, but I could imagine parsing the argument "sorted=True" could speed it up, such that it is possible to sort on `guest_name` and we do not need to loop through the entire dataset at each time, but we can stop after we see a new instance of `guest_name` 