gistfile1.ml

#light

module Map =
  let insertWith (f:'a -> 'a -> 'a) (k:'tkey) (v:'a) (m:Map<'tkey, 'a>) =
    match Map.tryfind k m with 
    | None   -> Map.add k v m
    | Some x -> let res = f v x
                Map.add k res m

// Gets recommendations for a person by using a weighted average
let getRecommendations
  (prefs:Map<string, Map<string, float>>)
  (person:string) 
  (similarity:Map<string, Map<string, float>> -> string -> string -> float) =
  
  let totals, simSums = 
    Map.fold_right (fun other _ acc -> if other <> person then
                                         let sim = similarity prefs person other
                                         if sim > 0. then 
                                           Map.fold_right (fun item _ acc' -> 
                                             if not (prefs.[person].ContainsKey item) || prefs.[person].[item] = 0. then
                                               let totals = Map.insertWith (+) item (prefs.[other].[item] * sim) (fst acc')
                                               let simSums = Map.insertWith (+) item sim (snd acc')
                                               (totals, simSums)
                                             else
                                               acc'
                                           ) prefs.[other] acc
                                         else acc
                                       else acc) prefs (Map.empty, Map.empty)
                                                                 
  [for kvp in totals -> (kvp.Value / simSums.[kvp.Key], kvp.Key)]
    |> List.sort_by fst
    |> List.rev