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let random_select (lst : 'a list) : 'a option =
if List.length lst = 0 then None
else Random.int (List.length lst) |> List.nth lst |> Option.some
let random_sample (size : int) (lst : 'a list) : 'a list =
let arr = Array.of_list lst in
let len = Array.length arr in
if len <= size then lst
else
let idxs = Hashtbl.create size in
let rec random_sample' lst_sample =
if List.length lst_sample = size then lst_sample
else
let idx = Random.int len in
if Hashtbl.mem idxs idx then random_sample' lst_sample
else (
Hashtbl.add idxs idx ();
random_sample' (arr.(idx) :: lst_sample))
in
random_sample' []
let random_sample_weighted (size : int) (probs : float list) (lst : 'a list) :
'a list =
List.combine probs lst
|> List.filter (fun (p, _) -> Random.float 1.0 < p)
|> List.map snd |> random_sample size
let shuffle (lst : 'a list) : 'a list =
let rec shuffle' (lst_shuffled : 'a list) (lst : 'a list) =
match lst with
| [] -> lst_shuffled
| _ ->
let idx_pick = Random.int (List.length lst) in
let item = List.nth lst idx_pick in
let lst = List.filteri (fun idx _ -> idx <> idx_pick) lst in
shuffle' (item :: lst_shuffled) lst
in
shuffle' [] lst