The dirtiest solution:

let to_array t =
 let a =  Array.make (Hashtbl.length t) (Obj.magic 0)  in
   ignore
     (Hashtbl.fold (fun k v i -> a.(i) <- (k, v); i + 1) t 0) ; 
     a  
 
 


Does it work correctly for floats? 

 

Looks good for floats. 
 
# let to_array t =
   let a =  Array.make (Hashtbl.length t) (Obj.magic 0)  in
     ignore
       (Hashtbl.fold (fun k v i -> a.(i) <- (k, v); i + 1) t 0) ;
       a
 
  ;;
val to_array : ('a, 'b) Hashtbl.t -> ('a * 'b) array = <fun>
# let h = Hashtbl.create 0;;
val h : ('_a, '_b) Hashtbl.t = <abstr>
# Hashtbl.add h 1.0 2.0;;
- : unit = ()
# to_array h;;
- : (float * float) array = [|(1., 2.)|]
# Gc.compact ();;
- : unit = ()
#
 
 BTW, the array should store a pointer to a tuple of two floats, so
I thinkt float or ints doesn't matter. I won't use this solution, because
 it isn't better than others. 

 Christoph Bauer