ff: "aggregate" function for ff matrix ?

Hello,

Playing around the ff package, I wonder if there are some possibilities 
to develop functions like "aggregate" based on the ffcolapply or ffapply 
ff functions, which would split the big ff matrix into subsets according 
to the different levels of a factorial vector, computes summary 
statistics for each level, and returns the result in a ff object ?

Thanks in advance.

Regards

Cl?ment Tisseuil