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Module Belt.Array ​

Belt.Array

mutable array: Utilities functions

Belt.Array Utililites for Array functions

type 'a t = 'a array
val length : 'a t -> int

length xs return the size of the array

val size : 'a t -> int

See length

val get : 'a t -> int -> 'a option

get arr i

If i <= 0 <= length arr;returns Some value where value is the item at index i If i is out of range;returns None

ocaml
  Belt.Array.get [|"a";"b";"c"|] 0 = Some "a";;
  Belt.Array.get [|"a";"b";"c"|] 3 = None;;
  Belt.Array.get [|"a";"b";"c"|] (-1) = None;;
val getExn : 'a t -> int -> 'a

getExn arr i

raise an exception if i is out of range;otherwise return the value at index i in arr

val getUnsafe : 'a t -> int -> 'a

getUnsafe arr i

Unsafe

no bounds checking;this would cause type error if i does not stay within range

val getUndefined : 'a t -> int -> 'a Js.undefined

getUndefined arr i

It does the samething in the runtime as getUnsafe; it is type safe since the return type still track whether it is in range or not

val set : 'a t -> int -> 'a -> bool

set arr n x modifies arr in place; it replaces the nth element of arr with x

returns false means not updated due to out of range

val setExn : 'a t -> int -> 'a -> unit

setExn arr i x raise an exception if i is out of range

val setUnsafe : 'a t -> int -> 'a -> unit
val shuffleInPlace : 'a t -> unit

shuffleInPlace arr randomly re-orders the items in arr

val shuffle : 'a t -> 'a t

shuffle xs

returns a fresh array with items in original array randomly shuffled

val reverseInPlace : 'a t -> unit

reverseInPlace arr reverses items in arr in place

ocaml
  let arr = [|10;11;12;13;14|];;
  let () = reverseInPlace arr;;
  arr = [|14;13;12;11;10|];;
val reverse : 'a t -> 'a t

reverse arr

returns a fresh array with items in arr in reverse order

ocaml
  reverse [|10;11;12;13;14|] = [|14;13;12;11;10|];;
val makeUninitialized : int -> 'a Js.undefined array

makeUninitialized n creates an array of length n filled with the undefined value. You must specify the type of data that will eventually fill the array.

ocaml
  let arr: string Js.undefined array = makeUninitialized 5;;
  getExn arr 0 = Js.undefined;;
val makeUninitializedUnsafe : int -> 'a t

`makeUninitializedUnsafe n`

Unsafe

ocaml
let arr = Belt.Array.makeUninitializedUnsafe 5;;
let () = Js.log(Belt.Array.getExn arr 0);; (* undefined *)
Belt.Array.setExn arr 0 "example";;
let () = Js.log(Belt.Array.getExn arr 0 = "example");;
val make : int -> 'a -> 'a t

make n e return an array of size n filled with value e

returns an empty array when n is negative.

val range : int -> int -> int t

range start finish create an inclusive array

ocaml
  range 0 3 =  [|0;1;2;3|];;
  range 3 0 =  [||] ;;
  range 3 3 = [|3|];;
val rangeBy : int -> int -> step:int -> int t

rangeBy start finish ~step

returns empty array when step is 0 or negative it also return empty array when start > finish

ocaml
 rangeBy 0 10 ~step:3 = [|0;3;6;9|];;
 rangeBy 0 12 ~step:3 = [|0;3;6;9;12|];;
 rangeBy 33 0 ~step:1 =  [||];;
 rangeBy 33 0 ~step:(-1) = [||];;
 rangeBy 3 12 ~step:(-1) = [||];;
 rangeBy 3 3 ~step:0 = [||] ;;
 rangeBy 3 3 ~step:(1) = [|3|] ;;
val makeByU : int -> (int -> 'a) Js.Fn.arity1 -> 'a t
val makeBy : int -> (int -> 'a) -> 'a t

makeBy n f

return an empty array when n is negative return an array of size n populated by f i start from 0 to n - 1

ocaml
  makeBy 5 (fun i -> i) = [|0;1;2;3;4|];;
  makeBy 5 (fun i -> i * i) = [|0;1;4;9;16|]
val makeByAndShuffleU : int -> (int -> 'a) Js.Fn.arity1 -> 'a t
val makeByAndShuffle : int -> (int -> 'a) -> 'a t

makeByAndShuffle n f

Equivalent to shuffle (makeBy n f)

val zip : 'a t -> 'b array -> ('a * 'b) array

zip a b

Create an array of pairs from corresponding elements of a and b. Stop with the shorter array

ocaml
  zip [|1;2|] [|3;4;5|] = [|(1, 3);(2, 4)|]
val zipByU : 'a t -> 'b array -> ('a -> 'b -> 'c) Js.Fn.arity2 -> 'c array
val zipBy : 'a t -> 'b array -> ('a -> 'b -> 'c) -> 'c array

zipBy xs ys f

Create an array by applying f to corresponding elements of xs and ys Stops with shorter array

Equivalent to map (zip xs ys) (fun (a,b) -> f a b)

ocaml
  zipBy [|1;2;3|] [|4;5|] (fun a b -> 2 * a + b) = [|6;9|];;
val unzip : ('a * 'b) array -> 'a t * 'b array

unzip a takes an array of pairs and creates a pair of arrays. The first array contains all the first items of the pairs; the second array contains all the second items.

ocaml
  unzip [|(1,2) ; (3,4)|] = ([|1;3|], [|2;4|]);;
  unzip [|(1,2) ; (3,4) ; (5,6) ; (7,8)|] = ([|1;3;5;7|], [|2;4;6;8|]);;
val concat : 'a t -> 'a t -> 'a t

concat xs ys

returns a fresh array containing the concatenation of the arrays v1 and v2;so even if v1 or v2 is empty;it can not be shared

ocaml
  concat [|1;2;3|] [|4;5|] = [|1;2;3;4;5|];;
  concat [| |] [|"a";"b";"c"|] = [|"a";"b";"c"|];;
val concatMany : 'a t t -> 'a t

concatMany xss

returns a fresh array as the concatenation of xss (an array of arrays)

ocaml
  concatMany [| [|1;2;3|]; [|4;5;6|]; [|7;8|] |] = [|1;2;3;4;5;6;7;8|];;
val slice : 'a t -> offset:int -> len:int -> 'a t

slice xs offset len creates a new array with the len elements of xs starting at offset for

offset can be negative;and is evaluated as length xs - offset slice xs -1 1 means get the last element as a singleton array

slice xs (-len) len will return a copy of the array

if the array does not have enough data;slice extracts through the end of sequence.

if len is negative;returns the empty array.

ocaml
  slice [|10;11;12;13;14;15;16|] ~offset: 2 ~len: 3 = [|12;13;14|];;
  slice [|10;11;12;13;14;15;16|] ~offset: (-4) ~len: 3 = [|13;14;15|];;
  slice [|10;11;12;13;14;15;16|] ~offset:4  ~len:9 = [|14;15;16|];;
val sliceToEnd : 'a t -> int -> 'a t

sliceToEnd xs offset creates a new array with the elements of xs starting at offset

offset can be negative;and is evaluated as length xs - offset sliceToEnd xs -1 means get the last element as a singleton array

sliceToEnd xs 0 will return a copy of the array

ocaml
  sliceToEnd [|10;11;12;13;14;15;16|] 2 = [|12;13;14;15;16|];;
  sliceToEnd [|10;11;12;13;14;15;16|] (-4) = [|13;14;15;16|];;
val copy : 'a t -> 'a t

copy a

returns a copy of a;that is;a fresh array containing the same elements as a.

val fill : 'a t -> offset:int -> len:int -> 'a -> unit

fill arr ~offset ~len x

Modifies arr in place, storing x in elements number offset to offset + len - 1.

offset can be negative;and is evaluated as length arr - offset

fill arr ~offset:(-1) ~len:1 means fill the last element, if the array does not have enough data;fill will ignore it

ocaml

  let arr = makeBy 5 (fun i -> i) ;;
  fill arr ~offset:2 ~len:2 9 ;;
  arr = [|0;1;9;9;4|];;
  fill arr ~offset:7 ~len:2 8;;
  arr = [|0;1;9;9;4|];;
val blit : 
  src:'a t ->
  srcOffset:int ->
  dst:'a t ->
  dstOffset:int ->
  len:int ->
  unit

blit ~src:v1 ~srcOffset:o1 ~dst:v2 ~dstOffset:o2 ~len

copies len elements from array v1;starting at element number o1;to array v2, starting at element number o2.

It works correctly even if v1 and v2 are the same array;and the source and destination chunks overlap.

offset can be negative;-1 means len - 1;if len + offset is still negative;it will be set as 0

For each of the examples;presume that v1 = [|10;11;12;13;14;15;16;17|] and v2 = [|20;21;22;23;24;25;26;27|]. The result shown is the content of the destination array.

ocaml
  Belt.Array.blit ~src: v1 ~srcOffset: 4 ~dst: v2 ~dstOffset: 2 ~len: 3 |.
    [|20;21;14;15;16;25;26;27|]
  Belt.Array.blit ~src: v1 ~srcOffset: 4 ~dst: v1 ~dstOffset: 2 ~len: 3 |.
    [|10;11;14;15;16;15;16;17|]
val blitUnsafe : 
  src:'a t ->
  srcOffset:int ->
  dst:'a t ->
  dstOffset:int ->
  len:int ->
  unit

Unsafe blit without bounds checking

val forEachU : 'a t -> ('a -> unit) Js.Fn.arity1 -> unit
val forEach : 'a t -> ('a -> unit) -> unit

forEach xs f

Call f on each element of xs from the beginning to end. f returns unit;so no new array is created. Use forEach when you are primarily concerned with repetitively creating side effects.

ocaml
  forEach [|"a";"b";"c"|] (fun x -> Js.log("Item: " ^ x));;
  (*  prints:
    Item: a
    Item: b
    Item: c
  *)

  let total = ref 0;;
  forEach [|1;2;3;4|] (fun x -> total := !total + x);;
  !total  = 1 + 2 + 3 + 4;;
val mapU : 'a t -> ('a -> 'b) Js.Fn.arity1 -> 'b array
val map : 'a t -> ('a -> 'b) -> 'b array

map xs f

returns a new array by calling f for each element of xs from the beginning to end

ocaml
 map [|1;2|] (fun x-> x + 10) = [|11;12|]
val flatMapU : 'a t -> ('a -> 'b t) Js.Fn.arity1 -> 'b t
val flatMap : 'a t -> ('a -> 'b t) -> 'b t

flatMap xs f **return** a new array by calling `f` for each element of `xs` from the beginning to end, and then concatenating the results ``` flatMap |1;2| (fun x-> |x + 10;x + 20|) = |11;21;12;22| ```

val getByU : 'a t -> ('a -> bool) Js.Fn.arity1 -> 'a option
val getBy : 'a t -> ('a -> bool) -> 'a option

getBy xs p returns Some value for the first value in xs that satisifies the predicate function p; returns None if no element satisifies the function.

ocaml
    getBy [|1;4;3;2|] (fun x -> x mod 2 = 0) = Some 4
    getBy [|15;13;11|] (fun x -> x mod 2 = 0) = None
val getIndexByU : 'a t -> ('a -> bool) Js.Fn.arity1 -> int option
val getIndexBy : 'a t -> ('a -> bool) -> int option

getIndexBy xs p returns Some index for the first value in xs that satisifies the predicate function p; returns None if no element satisifies the function.

ocaml
    getIndexBy [|1;4;3;2|] (fun x -> x mod 2 = 0) = Some 1
    getIndexBy [|15;13;11|] (fun x -> x mod 2 = 0) = None
val keepU : 'a t -> ('a -> bool) Js.Fn.arity1 -> 'a t
val keep : 'a t -> ('a -> bool) -> 'a t

keep xs p

returns a new array that keeps all elements satisfying p

ocaml
  keep [|1;2;3|] (fun x -> x mod  2 = 0) = [|2|]
val keepWithIndexU : 'a t -> ('a -> int -> bool) Js.Fn.arity2 -> 'a t
val keepWithIndex : 'a t -> ('a -> int -> bool) -> 'a t

keepWithIndex xs p

returns a new array that keeps all elements satisfying p. The predicate p takes two arguments: the element from xs and the index starting from 0.

ocaml
  keepWithIndex [|1;2;3|] (fun _x i -> i = 1) = [|2|]
val keepMapU : 'a t -> ('a -> 'b option) Js.Fn.arity1 -> 'b array
val keepMap : 'a t -> ('a -> 'b option) -> 'b array

keepMap xs p

returns a new array that keeps all elements that return a non-None when applied to p

ocaml
  keepMap [|1;2;3|] (fun x -> if x mod 2 = 0 then Some x else None)
  = [| 2 |]
val forEachWithIndexU : 'a t -> (int -> 'a -> unit) Js.Fn.arity2 -> unit
val forEachWithIndex : 'a t -> (int -> 'a -> unit) -> unit

forEachWithIndex xs f

The same as forEach; except that f is supplied with two arguments: the index starting from 0 and the element from xs

ocaml

  forEachWithIndex [|"a";"b";"c"|] (fun i x -> Js.log("Item " ^ (string_of_int i) ^ " is " ^ x));;
  (*  prints:
    Item 0 is a
    Item 1 is b
    Item 2 is c
  *)

  let total = ref 0 ;;
  forEachWithIndex [|10;11;12;13|] (fun i x -> total := !total + x + i);;
  !total  = 0 + 10 + 1 +  11 + 2 + 12 + 3 + 13;;
val mapWithIndexU : 'a t -> (int -> 'a -> 'b) Js.Fn.arity2 -> 'b t
val mapWithIndex : 'a t -> (int -> 'a -> 'b) -> 'b t

mapWithIndex xs f applies f to each element of xs. Function f takes two arguments: the index starting from 0 and the element from xs.

ocaml
  mapWithIndex [|1;2;3|] (fun i x -> i + x) =
  [|0 + 1; 1 + 2; 2 + 3|]
val partitionU : 'a t -> ('a -> bool) Js.Fn.arity1 -> 'a t * 'a t
val partition : 'a t -> ('a -> bool) -> 'a t * 'a t

partition f a split array into tuple of two arrays based on predicate f; first of tuple where predicate cause true, second where predicate cause false

ocaml
  partition [|1;2;3;4;5|] (fun x -> x mod 2 = 0  ) = ([|2;4|], [|1;2;3|]);;
  partition [|1;2;3;4;5|] (fun x -> x mod 2 <> 0 ) = ([|1;2;3|], [|2;4|]);;
val reduceU : 'b array -> 'a -> ('a -> 'b -> 'a) Js.Fn.arity2 -> 'a
val reduce : 'b array -> 'a -> ('a -> 'b -> 'a) -> 'a

reduce xs init f

Applies f to each element of xs from beginning to end. Function f has two parameters: the item from the list and an “accumulator”;which starts with a value of init. reduce returns the final value of the accumulator.

ocaml
  reduce [|2;3;4|] 1 (+) = 10;;
  reduce [|"a";"b";"c";"d"|] "" (^) = "abcd";;
val reduceReverseU : 'b array -> 'a -> ('a -> 'b -> 'a) Js.Fn.arity2 -> 'a
val reduceReverse : 'b array -> 'a -> ('a -> 'b -> 'a) -> 'a

reduceReverse xs init f

Works like reduce;except that function f is applied to each item of xs from the last back to the first.

ocaml
  reduceReverse [|"a";"b";"c";"d"|] "" (^) = "dcba";;
val reduceReverse2U : 
  'a t ->
  'b array ->
  'c ->
  ('c -> 'a -> 'b -> 'c) Js.Fn.arity3 ->
  'c
val reduceReverse2 : 'a t -> 'b array -> 'c -> ('c -> 'a -> 'b -> 'c) -> 'c

reduceReverse2 xs ys init f Reduces two arrays xs and ys;taking items starting at min (length xs) (length ys) down to and including zero.

ocaml
  reduceReverse2 [|1;2;3|] [|1;2|] 0 (fun acc x y -> acc + x + y) = 6
val reduceWithIndexU : 'a t -> 'b -> ('b -> 'a -> int -> 'b) Js.Fn.arity3 -> 'b
val reduceWithIndex : 'a t -> 'b -> ('b -> 'a -> int -> 'b) -> 'b

reduceWithIndex xs f

Applies f to each element of xs from beginning to end. Function f has three parameters: the item from the array and an “accumulator”, which starts with a value of init and the index of each element. reduceWithIndex returns the final value of the accumulator.

ocaml
  reduceWithIndex [|1;2;3;4|] 0 (fun acc x i -> acc + x + i) = 16;
val joinWithU : 'a t -> string -> ('a -> string) Js.Fn.arity1 -> string
val joinWith : 'a t -> string -> ('a -> string) -> string

joinWith xs sep toString

Concatenates all the elements of xs converted to string with toString, each separated by sep, the string given as the second argument, into a single string. If the array has only one element, then that element will be returned without using the separator. If the array is empty, the empty string will be returned.

ocaml
  joinWith [|0; 1|] ", " string_of_int = "0, 1"
  joinWith [||] " " string_of_int = ""
  joinWith [|1|] " " string_of_int = "1"
val someU : 'a t -> ('a -> bool) Js.Fn.arity1 -> bool
val some : 'a t -> ('a -> bool) -> bool

some xs p

returns true if at least one of the elements in xs satifies p;where p is a predicate: a function taking an element and returning a bool.

ocaml
  some [|2; 3; 4|] (fun x -> x mod 2 = 1) = true;;
  some [|-1; -3; -5|] (fun x -> x > 0) = false;;
val everyU : 'a t -> ('a -> bool) Js.Fn.arity1 -> bool
val every : 'a t -> ('a -> bool) -> bool

every xs p

returns true if all elements satisfy p;where p is a predicate: a function taking an element and returning a bool.

ocaml
  every [|1; 3; 5|] (fun x -> x mod 2 = 1) = true;;
  every [|1; -3; 5|] (fun x -> x > 0) = false;;
val every2U : 'a t -> 'b t -> ('a -> 'b -> bool) Js.Fn.arity2 -> bool
val every2 : 'a t -> 'b t -> ('a -> 'b -> bool) -> bool

every2 xs ys p returns true if p xi yi is true for all pairs of elements up to the shorter length (i.e. min (length xs) (length ys))

ocaml
  every2 [|1;2;3|] [|0;1|] (>) = true;;
  every2 [||] [|1|] (fun  x y -> x > y) = true;;
  every2 [|2;3|] [|1|] (fun  x y -> x > y) = true;;
  every2 [|0;1|] [|5;0|] (fun x y -> x > y) = false;
val some2U : 'a t -> 'b t -> ('a -> 'b -> bool) Js.Fn.arity2 -> bool
val some2 : 'a t -> 'b t -> ('a -> 'b -> bool) -> bool

some2 xs ys p returns true if p xi yi is true for any pair of elements up to the shorter length (i.e. min (length xs) (length ys))

ocaml
  some2 [|0;2|] [|1;0;3|] (>) = true ;;
  (some2 [||] [|1|] (fun   x y -> x > y)) =  false;;
  (some2 [|2;3|] [|1;4|] (fun   x y -> x > y)) = true;;
val cmpU : 'a t -> 'a t -> ('a -> 'a -> int) Js.Fn.arity2 -> int
val cmp : 'a t -> 'a t -> ('a -> 'a -> int) -> int

cmp xs ys f

  • Compared by length if length xs <> length ys;returning -1 iflength xs < length ys or 1 if length xs > length ys
  • Otherwise compare one by one f x y. f returns
  • a negative number if x is “less than” y
  • zero if x is “equal to” y
  • a positive number if x is “greater than” y
  • The comparison returns the first non-zero result of f;or zero if f returns zero for all x and y.
ocaml
  cmp [|1; 3; 5|] [|1; 4; 2|] (fun a b -> compare a b) = -1;;
  cmp [|1; 3; 5|] [|1; 2; 3|] (fun a b -> compare a b) = 1;;
  cmp [|1; 3; 5|] [|1; 3; 5|] (fun a b -> compare a b) = 0;;
val eqU : 'a t -> 'a t -> ('a -> 'a -> bool) Js.Fn.arity2 -> bool
val eq : 'a t -> 'a t -> ('a -> 'a -> bool) -> bool

eq xs ys

  • return false if length is not the same
  • otherwise compare items one by one using f xi yi;and return true if all results are true;false otherwise
ocaml
  eq [|1; 2; 3|] [|-1; -2; -3|] (fun a b -> abs a = abs b) = true
val truncateToLengthUnsafe : 'a t -> int -> unit

Unsafe truncateToLengthUnsafe xs n sets length of array xs to n.

If n is greater than the length of xs;the extra elements are set to Js.Null_undefined.null

If n is less than zero;raises a RangeError.

ocaml
  let arr = [|"ant";"bee";"cat";"dog";"elk"|];;
  let () = truncateToLengthUnsafe arr 3;;
  arr = [|"ant";"bee";"cat"|];;
val initU : int -> (int -> 'a) Js.Fn.arity1 -> 'a t
val init : int -> (int -> 'a) -> 'a t
val push : 'a t -> 'a -> unit

arr->push(item) push element `item` into the array