Hello,
There should be some way to compile quartiles in a map/reduce fashion (i.e. with api similar to Pig's Arithmetic custom function) without keeping enormous count hash? There's this countsketch thing that i implemented before on map reduce, but it is sort of like bloom filter: if it gives a wrong result, the error is fairly huge (in case of bloom filter, 100%) and to get good results it still requires quite a bit of memory
