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Source file owl_dataframe.ml

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# 1 "src/base/misc/owl_dataframe.ml"
(*
 * OWL - OCaml Scientific and Engineering Computing
 * Copyright (c) 2016-2020 Liang Wang <liang.wang@cl.cam.ac.uk>
 *)

open Owl_types

type elt =
  | Bool   of bool
  | Int    of int
  | Float  of float
  | String of string
  | Any

type series =
  | Bool_Series   of bool array
  | Int_Series    of int array
  | Float_Series  of float array
  | String_Series of string array
  | Any_Series

type t =
  { mutable data : series array
  ; (* column-based table, each column is a time series *)
    mutable head : (string, int) Hashtbl.t
  ; (* head and index of each column, stored in a hash table *)
    mutable used : int
  ; (* sise of the used buffer space *)
    mutable size : int (* size of the allocated buffer *)
  }

let unpack_bool = function
  | Bool x -> x
  | _      -> raise Owl_exception.NOT_SUPPORTED


let unpack_int = function
  | Int x -> x
  | _     -> raise Owl_exception.NOT_SUPPORTED


let unpack_float = function
  | Float x -> x
  | _       -> raise Owl_exception.NOT_SUPPORTED


let unpack_string = function
  | String x -> x
  | _        -> raise Owl_exception.NOT_SUPPORTED


let unpack_bool_series = function
  | Bool_Series x -> x
  | _             -> raise Owl_exception.NOT_SUPPORTED


let unpack_int_series = function
  | Int_Series x -> x
  | _            -> raise Owl_exception.NOT_SUPPORTED


let unpack_float_series = function
  | Float_Series x -> x
  | _              -> raise Owl_exception.NOT_SUPPORTED


let unpack_string_series = function
  | String_Series x -> x
  | _               -> raise Owl_exception.NOT_SUPPORTED


let pack_bool x = Bool x

let pack_int x = Int x

let pack_float x = Float x

let pack_string x = String x

let pack_bool_series x = Bool_Series x

let pack_int_series x = Int_Series x

let pack_float_series x = Float_Series x

let pack_string_series x = String_Series x

let allocate_space data =
  Array.(
    map
      (function
        | Bool_Series c   -> Bool_Series (append c (copy c))
        | Int_Series c    -> Int_Series (append c (copy c))
        | Float_Series c  -> Float_Series (append c (copy c))
        | String_Series c -> String_Series (append c (copy c))
        | Any_Series      -> Any_Series)
      data)


let set_elt_in_series x i = function
  | Bool a   -> (unpack_bool_series x).(i) <- a
  | Int a    -> (unpack_int_series x).(i) <- a
  | Float a  -> (unpack_float_series x).(i) <- a
  | String a -> (unpack_string_series x).(i) <- a
  | Any      -> ()


let get_elt_in_series x i =
  match x with
  | Bool_Series c   -> Bool c.(i)
  | Int_Series c    -> Int c.(i)
  | Float_Series c  -> Float c.(i)
  | String_Series c -> String c.(i)
  | Any_Series      -> Any


let init_series n = function
  | Bool a   -> Bool_Series (Array.make n a)
  | Int a    -> Int_Series (Array.make n a)
  | Float a  -> Float_Series (Array.make n a)
  | String a -> String_Series (Array.make n a)
  | Any      -> Any_Series


let resize_series n = function
  | Bool_Series c   -> Bool_Series (Owl_utils_array.resize ~head:true true n c)
  | Int_Series c    -> Int_Series (Owl_utils_array.resize ~head:true 0 n c)
  | Float_Series c  -> Float_Series (Owl_utils_array.resize ~head:true 0. n c)
  | String_Series c -> String_Series (Owl_utils_array.resize ~head:true "" n c)
  | Any_Series      -> Any_Series


let append_series x y =
  match x, y with
  | Bool_Series x, Bool_Series y -> Bool_Series (Array.append x y)
  | Int_Series x, Int_Series y -> Int_Series (Array.append x y)
  | Float_Series x, Float_Series y -> Float_Series (Array.append x y)
  | String_Series x, String_Series y -> String_Series (Array.append x y)
  | Any_Series, Any_Series -> Any_Series
  | _ -> failwith "append_series: unsupported type"


let length_series = function
  | Bool_Series c   -> Array.length c
  | Int_Series c    -> Array.length c
  | Float_Series c  -> Array.length c
  | String_Series c -> Array.length c
  | Any_Series      -> 0


let slice_series slice = function
  | Bool_Series c   -> Bool_Series (Owl_utils_array.get_slice slice c)
  | Int_Series c    -> Int_Series (Owl_utils_array.get_slice slice c)
  | Float_Series c  -> Float_Series (Owl_utils_array.get_slice slice c)
  | String_Series c -> String_Series (Owl_utils_array.get_slice slice c)
  | Any_Series      -> Any_Series


let argsort_series = function
  | Bool_Series c   -> Owl_utils_array.argsort ~cmp:Stdlib.compare c
  | Int_Series c    -> Owl_utils_array.argsort ~cmp:Stdlib.compare c
  | Float_Series c  -> Owl_utils_array.argsort ~cmp:Stdlib.compare c
  | String_Series c -> Owl_utils_array.argsort ~cmp:Stdlib.compare c
  | Any_Series      -> [||]


let min_series = function
  | Bool_Series c   -> Owl_utils_array.min_i ~cmp:Stdlib.compare c
  | Int_Series c    -> Owl_utils_array.min_i ~cmp:Stdlib.compare c
  | Float_Series c  -> Owl_utils_array.min_i ~cmp:Stdlib.compare c
  | String_Series c -> Owl_utils_array.min_i ~cmp:Stdlib.compare c
  | Any_Series      -> -1


let max_series = function
  | Bool_Series c   -> Owl_utils_array.max_i ~cmp:Stdlib.compare c
  | Int_Series c    -> Owl_utils_array.max_i ~cmp:Stdlib.compare c
  | Float_Series c  -> Owl_utils_array.max_i ~cmp:Stdlib.compare c
  | String_Series c -> Owl_utils_array.max_i ~cmp:Stdlib.compare c
  | Any_Series      -> -1


let remove_ith_elt i = function
  | Bool_Series c   -> Bool_Series (Owl_utils_array.remove c i)
  | Int_Series c    -> Int_Series (Owl_utils_array.remove c i)
  | Float_Series c  -> Float_Series (Owl_utils_array.remove c i)
  | String_Series c -> String_Series (Owl_utils_array.remove c i)
  | Any_Series      -> Any_Series


let insert_ith_elt i e = function
  | Bool_Series c   -> Bool_Series (Owl_utils_array.insert c [| unpack_bool e |] i)
  | Int_Series c    -> Int_Series (Owl_utils_array.insert c [| unpack_int e |] i)
  | Float_Series c  -> Float_Series (Owl_utils_array.insert c [| unpack_float e |] i)
  | String_Series c -> String_Series (Owl_utils_array.insert c [| unpack_string e |] i)
  | Any_Series      -> Any_Series


let get_ith_elt i = function
  | Bool_Series c   -> Bool c.(i)
  | Int_Series c    -> Int c.(i)
  | Float_Series c  -> Float c.(i)
  | String_Series c -> String c.(i)
  | Any_Series      -> Any


let elt_to_str = function
  | Bool a   -> string_of_bool a
  | Int a    -> string_of_int a
  | Float a  -> string_of_float a
  | String a -> a
  | Any      -> ""


let series_type_to_str = function
  | Bool_Series _c   -> "b"
  | Int_Series _c    -> "i"
  | Float_Series _c  -> "f"
  | String_Series _c -> "s"
  | Any_Series       -> "a"


let str_to_elt_fun = function
  | "b" -> fun a -> Bool (bool_of_string a)
  | "i" -> fun a -> Int (int_of_string a)
  | "f" -> fun a -> if a = "" then Float nan else Float (float_of_string a)
  | "s" -> fun a -> String a
  | _   -> failwith "str_to_elt_fun: unsupported type"


let elt_array_to_series typ x =
  match typ with
  | Bool_Series _   -> pack_bool_series (Array.map unpack_bool x)
  | Int_Series _    -> pack_int_series (Array.map unpack_int x)
  | Float_Series _  -> pack_float_series (Array.map unpack_float x)
  | String_Series _ -> pack_string_series (Array.map unpack_string x)
  | Any_Series      -> Any_Series


let make ?data head_names =
  let col_num = Array.length head_names in
  let head = Hashtbl.create 64 in
  (* check the head names are unique *)
  Array.iteri
    (fun i s ->
      assert (Hashtbl.mem head s = false);
      Hashtbl.add head s i)
    head_names;
  let data =
    match data with
    | Some a -> a
    | None   -> Array.make col_num Any_Series
  in
  assert (Array.length data = col_num);
  (* calculate the actual number of rows *)
  let size = if col_num = 0 then 0 else length_series data.(0) in
  let used = size in
  (* check all the series have the same length *)
  Array.iter (fun c -> assert (length_series c = size)) data;
  (* return the generated frame *)
  { data; head; used; size }


let col_num x = Array.length x.data

let row_num x = x.used

let shape x = row_num x, col_num x

let numel x = row_num x * col_num x

let types x = Array.map series_type_to_str x.data

let append_row x row =
  assert (col_num x = Array.length row);
  if x.size = 0
  then (
    let n = 16 in
    x.data <- Array.map (init_series n) row;
    x.size <- n;
    x.used <- 1)
  else (
    if x.used = x.size
    then (
      x.data <- allocate_space x.data;
      x.size <- length_series x.data.(0));
    Array.iteri (fun i a -> set_elt_in_series x.data.(i) x.used a) row;
    x.used <- x.used + 1)


let append_col x col head =
  let m, n = shape x in
  assert (m = length_series col);
  let col = resize_series x.size col in
  Hashtbl.add x.head head n;
  x.data <- Array.append x.data [| col |]


let get_heads x =
  let kv = Hashtbl.fold (fun k v acc -> Array.append acc [| k, v |]) x.head [||] in
  Array.sort (fun a b -> snd a - snd b) kv;
  Array.map fst kv


let set_heads x head_names =
  assert (Array.length head_names = Array.length x.data);
  let head = Hashtbl.create 64 in
  Array.iteri
    (fun i s ->
      assert (Hashtbl.mem head s = false);
      Hashtbl.add head s i)
    head_names;
  x.head <- head


let remove_row x i =
  let i = Owl_utils_ndarray.adjust_index i (row_num x) in
  let new_data = Array.map (fun s -> remove_ith_elt i s) x.data in
  x.data <- new_data;
  x.used <- x.used - 1;
  x.size <- x.size - 1


let remove_col x j =
  let j = Owl_utils_ndarray.adjust_index j (col_num x) in
  x.data <- Owl_utils_array.filteri (fun i _ -> i <> j) x.data;
  let new_head = Owl_utils_array.filteri (fun i _ -> i <> j) (get_heads x) in
  set_heads x new_head


let insert_row x i row =
  let i = Owl_utils_ndarray.adjust_index i (row_num x) in
  if x.size = 0
  then (
    let n = 16 in
    x.data <- Array.map (init_series n) row;
    x.size <- n;
    x.used <- 1)
  else (
    if x.used = x.size
    then (
      x.data <- allocate_space x.data;
      x.size <- length_series x.data.(0));
    let new_data = Array.mapi (fun j s -> insert_ith_elt i row.(j) s) x.data in
    x.data <- new_data;
    x.used <- x.used + 1;
    x.size <- x.size + 1)


let insert_col x j col_head col =
  let j = Owl_utils_ndarray.adjust_index j (col_num x) in
  let new_data = Owl_utils_array.insert x.data [| col |] j in
  x.data <- new_data;
  let new_head = Owl_utils_array.insert (get_heads x) [| col_head |] j in
  set_heads x new_head


let id_to_head x i = (get_heads x).(i)

let head_to_id x name = Hashtbl.find x.head name

let get_row x i = Array.map (fun y -> get_elt_in_series y i) x.data

let get_col x j =
  match x.data.(j) with
  | Bool_Series c   -> Bool_Series (Array.sub c 0 x.used)
  | Int_Series c    -> Int_Series (Array.sub c 0 x.used)
  | Float_Series c  -> Float_Series (Array.sub c 0 x.used)
  | String_Series c -> String_Series (Array.sub c 0 x.used)
  | Any_Series      -> Any_Series


let get_rows x idx = Array.map (get_row x) idx

let get_cols x idx = Array.map (get_col x) idx

(* TODO *)
let _get_row_assoc _x _idx =
  raise (Owl_exception.NOT_IMPLEMENTED "owl_dataframe._get_row_assoc")


let get_col_by_name x name =
  let j = Hashtbl.find x.head name in
  get_col x j


let get_cols_by_name x names = Array.map (get_col_by_name x) names

let get x i j =
  match x.data.(j) with
  | Bool_Series c   -> Bool c.(i)
  | Int_Series c    -> Int c.(i)
  | Float_Series c  -> Float c.(i)
  | String_Series c -> String c.(i)
  | Any_Series      -> Any


let set x i j a =
  match x.data.(j) with
  | Bool_Series c   -> c.(i) <- unpack_bool a
  | Int_Series c    -> c.(i) <- unpack_int a
  | Float_Series c  -> c.(i) <- unpack_float a
  | String_Series c -> c.(i) <- unpack_string a
  | Any_Series      -> ()


let get_by_name x i name =
  let j = Hashtbl.find x.head name in
  get x i j


let set_by_name x i name a =
  let j = Hashtbl.find x.head name in
  set x i j a


let to_cols x = x.data

let to_rows x =
  let stack = Owl_utils.Stack.make () in
  let m = row_num x in
  for i = 0 to m - 1 do
    Owl_utils.Stack.push stack (get_row x i)
  done;
  Owl_utils.Stack.to_array stack


let copy x =
  let head = Hashtbl.copy x.head in
  let used = x.used in
  let size = x.size in
  let data =
    Array.map
      (function
        | Bool_Series c   -> Bool_Series (Array.copy c)
        | Int_Series c    -> Int_Series (Array.copy c)
        | Float_Series c  -> Float_Series (Array.copy c)
        | String_Series c -> String_Series (Array.copy c)
        | Any_Series      -> Any_Series)
      x.data
  in
  { data; head; used; size }


let copy_struct x =
  let head = Hashtbl.copy x.head in
  let used = 0 in
  let size = 0 in
  let data =
    Array.map
      (function
        | Bool_Series _c   -> Bool_Series [||]
        | Int_Series _c    -> Int_Series [||]
        | Float_Series _c  -> Float_Series [||]
        | String_Series _c -> String_Series [||]
        | Any_Series       -> Any_Series)
      x.data
  in
  { data; head; used; size }


let reset x =
  x.used <- 0;
  x.size <- 0;
  x.data
    <- Array.map
         (function
           | Bool_Series _c   -> Bool_Series [||]
           | Int_Series _c    -> Int_Series [||]
           | Float_Series _c  -> Float_Series [||]
           | String_Series _c -> String_Series [||]
           | Any_Series       -> Any_Series)
         x.data


let concat_horizontal x y =
  assert (row_num x = row_num y);
  let head = Hashtbl.copy x.head in
  let col_num_x = col_num x in
  Hashtbl.iter (fun k v -> Hashtbl.add head k (v + col_num_x)) y.head;
  let col_num_y = col_num y in
  let data = Array.make (col_num_x + col_num_y) Any_Series in
  let size = max x.size y.size in
  for i = 0 to col_num_x - 1 do
    data.(i) <- resize_series size x.data.(i)
  done;
  for i = 0 to col_num_y - 1 do
    data.(col_num_x + i) <- resize_series size y.data.(i)
  done;
  { data; head; used = x.used; size }


let concat_vertical x y =
  assert (col_num x = col_num y);
  let head = Hashtbl.copy x.head in
  let used = x.used + y.used in
  let data = Array.make (col_num x) Any_Series in
  for i = 0 to col_num x - 1 do
    let sx = get_col x i in
    let j = id_to_head x i |> head_to_id y in
    let sy = get_col y j in
    data.(i) <- append_series sx sy
  done;
  { data; head; used; size = used }


let iteri_row f x =
  let m = row_num x in
  for i = 0 to m - 1 do
    f i (get_row x i)
  done


let iter_row f x = iteri_row (fun _ row -> f row) x

let mapi_row f x =
  let head = Hashtbl.copy x.head in
  let used = 0 in
  let size = 0 in
  let data = Array.map (fun _ -> Any_Series) x.data in
  let y = { data; head; used; size } in
  iteri_row (fun i row -> append_row y (f i row)) x;
  y


let map_row f x = mapi_row (fun _ row -> f row) x

let filteri_row f x =
  let head = Hashtbl.copy x.head in
  let used = 0 in
  let size = 0 in
  let data = Array.map (fun _ -> Any_Series) x.data in
  let y = { data; head; used; size } in
  iteri_row (fun i row -> if f i row = true then append_row y row) x;
  y


let filter_row f x = filteri_row (fun _ row -> f row) x

let filter_mapi_row f x =
  let head = Hashtbl.copy x.head in
  let used = 0 in
  let size = 0 in
  let data = Array.map (fun _ -> Any_Series) x.data in
  let y = { data; head; used; size } in
  iteri_row
    (fun i row ->
      match f i row with
      | Some r -> append_row y r
      | None   -> ())
    x;
  y


let filter_map_row f x = filter_mapi_row (fun _ row -> f row) x

let get_slice slice x =
  let slice = Array.(map of_list (of_list slice)) |> Array.map (fun s -> R_ s) in
  let shp_x = [| row_num x; col_num x |] in
  let _tmp0 = Owl_base_slicing.check_slice_definition slice shp_x in
  let slice =
    Array.map
      (function
        | R_ s -> s
        | _    -> failwith "get_slice: unsupported")
      _tmp0
  in
  let name = Owl_utils_array.get_slice slice.(1) (get_heads x) in
  let data =
    Array.map (head_to_id x) name |> get_cols x |> Array.map (slice_series slice.(0))
  in
  let used = length_series data.(0) in
  let head = Hashtbl.create (Array.length name) in
  Array.iteri (fun i s -> Hashtbl.add head s i) name;
  { data; head; used; size = used }


(* TODO *)
let _set_slice _x = raise (Owl_exception.NOT_IMPLEMENTED "owl_dataframe._set_slice")

let get_slice_by_name slice x =
  let row_slice = Array.of_list (fst slice) in
  let col_slice = Array.of_list (snd slice) in
  let shp_x = [| row_num x; col_num x |] in
  let refmt = Owl_base_slicing.check_slice_definition [| R_ row_slice |] shp_x in
  let row_slice =
    (function
      | R_ s -> s
      | _    -> failwith "get_slice: unsupported")
      refmt.(0)
  in
  let col_slice = if Array.length col_slice = 0 then get_heads x else col_slice in
  let data = Array.map (slice_series row_slice) (get_cols_by_name x col_slice) in
  let used = length_series data.(0) in
  let head = Hashtbl.create (Array.length col_slice) in
  Array.iteri (fun i s -> Hashtbl.add head s i) col_slice;
  { data; head; used; size = used }


(* TODO *)
let _set_slice_by_name _x =
  raise (Owl_exception.NOT_IMPLEMENTED "owl_dataframe._set_slice_by_name")


let head n x =
  let m = row_num x in
  assert (n > 0 && n <= m);
  get_slice [ [ 0; n - 1 ]; [] ] x


let tail n x =
  let m = row_num x in
  assert (n > 0 && n <= m);
  get_slice [ [ -n; -1 ]; [] ] x


let min_i x head =
  let series = get_col_by_name x head in
  min_series series


let max_i x head =
  let series = get_col_by_name x head in
  max_series series


let sort ?(inc = true) x head =
  let series = get_col_by_name x head in
  let indices = argsort_series series in
  if inc = false then Owl_utils_array.reverse indices;
  let y = copy_struct x in
  Array.iter (fun i -> get_row x i |> append_row y) indices;
  y


let unique x head =
  let series = get_col_by_name x head in
  let s_size = length_series series in
  let h_size = max 64 (s_size / 2) in
  let htbl = Hashtbl.create h_size in
  let stack = Owl_utils_stack.make () in
  for i = 0 to s_size - 1 do
    let k = get_ith_elt i series in
    if Hashtbl.mem htbl k = false
    then (
      Hashtbl.add htbl k None;
      Owl_utils_stack.push stack k)
  done;
  let elt_array = Owl_utils_stack.to_array stack in
  elt_array_to_series series elt_array


(* FIXME: not finished ... *)
let _join ?on ?how x =
  let on =
    match on with
    | Some a -> head_to_id x a
    | None   -> 0
  in
  let how =
    match how with
    | Some a -> a
    | None   -> `Inner
  in
  on, how


(* I/O functions *)

let guess_separator lines =
  let sep = [| ','; ' '; '\t'; ';'; ':'; '|' |] in
  (* rank by dividing as many parts as possible *)
  let tmp =
    Array.map
      (fun c ->
        let l = String.split_on_char c lines.(0) in
        c, List.length l)
      sep
  in
  (* sort by decreasing order *)
  Array.sort (fun a b -> snd b - snd a) tmp;
  let sep = Array.map fst tmp in
  let not_sep = ref true in
  let sep_idx = ref 0 in
  while !not_sep = true do
    let c = sep.(!sep_idx) in
    let n = String.split_on_char c lines.(0) |> List.length in
    (try
       Array.iter
         (fun line ->
           let m = String.split_on_char c line |> List.length in
           if m <> n then raise Owl_exception.FOUND)
         lines;
       not_sep := false
     with
    | _exn -> ());
    if !not_sep = true then sep_idx := !sep_idx + 1
  done;
  (* if cannot detect, return comma as default sep *)
  if !not_sep = false then sep.(!sep_idx) else ','


let guess_types sep lines =
  (* Note: no need to add "s" since it is default type *)
  let typ = [| "b"; "i"; "f" |] in
  let num_lines = Array.length lines in
  (* at least two lines because the first one will be dropped *)
  assert (num_lines > 1);
  let num_cols = lines.(0) |> String.trim |> String.split_on_char sep |> List.length in
  (* split into separate columns *)
  let stacks = Array.init num_cols (fun _ -> Owl_utils_stack.make ()) in
  Array.iteri
    (fun i line ->
      if i > 0
      then
        String.trim line
        |> String.split_on_char sep
        |> List.iteri (fun i c -> Owl_utils_stack.push stacks.(i) c))
    lines;
  let cols = Array.map Owl_utils_stack.to_array stacks in
  (* guess the types of columns *)
  Array.mapi
    (fun _i col ->
      let guess_typ = ref "s" in
      (try
         Array.iter
           (fun col_typ ->
             let typ_fun = str_to_elt_fun col_typ in
             let wrong_guess = ref false in
             (try
                Array.iter
                  (fun x ->
                    let y = String.trim x in
                    typ_fun y |> ignore)
                  col
              with
             | _exn -> wrong_guess := true);
             if !wrong_guess = false
             then (
               guess_typ := col_typ;
               raise Owl_exception.FOUND))
           typ
       with
      | _exn -> ());
      !guess_typ)
    cols


let of_csv ?sep ?head ?types fname =
  let lines = Owl_io.head 100 fname in
  let sep =
    match sep with
    | Some a -> a
    | None   -> guess_separator lines
  in
  let head_i = 0 in
  let head_names =
    match head with
    | Some a -> a
    | None   -> Owl_io.csv_head ~sep head_i fname
  in
  let types =
    match types with
    | Some a -> a
    | None   -> guess_types sep lines
  in
  assert (Array.length head_names = Array.length types);
  let convert_f = Array.map str_to_elt_fun types in
  let dataframe = make head_names in
  let dropped_line = ref 0 in
  Owl_io.read_csv_proc
    ~sep
    (fun i line ->
      try
        if i <> head_i
        then (
          let row = Array.map2 (fun f a -> f a) convert_f line in
          append_row dataframe row)
      with
      | _exn ->
        dropped_line := !dropped_line + 1;
        Owl_log.warn "of_csv: fail to parse line#%i @ %s" i fname)
    fname;
  if !dropped_line > 0 then Owl_log.warn "%i lines have been dropped." !dropped_line;
  dataframe


let to_csv ?sep x fname =
  let m, n = shape x in
  (* include heads as the first line *)
  let csv = Array.make_matrix (m + 1) n "" in
  csv.(0) <- get_heads x;
  (* dump the data into the table *)
  for i = 0 to m - 1 do
    for j = 0 to n - 1 do
      csv.(i + 1).(j) <- elt_to_str (get x i j)
    done
  done;
  Owl_io.write_csv ?sep csv fname


(* let print x = Owl_pretty.pp_dataframe Format.std_formatter x *)

let ( .%() ) x idx = get_by_name x (fst idx) (snd idx)

let ( .%()<- ) x idx a = set_by_name x (fst idx) (snd idx) a

let ( .?() ) x f = filter_row f x

let ( .?()<- ) x f g = filter_map_row (fun r -> if f r = true then Some (g r) else None) x

let ( .$() ) x slice = get_slice_by_name slice x

(* TODO *)
let[@warning "-32"] ( .$()<- ) _x _idx _a =
  raise (Owl_exception.NOT_IMPLEMENTED "owl_dataframe.( .$( )<- )")

(* ends here *)
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