Module `Belt.Array`

Belt.Array

mutable array: Utilities functions

Belt.Array Utililites for Array functions

type t('a) = array('a);

let length: t('a) => int;

length xs return the size of the array

let size: t('a) => int;

See length

let get: t('a) => int => option('a);

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;;

let getExn: t('a) => int => 'a;

getExn arr i

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

let getUnsafe: t('a) => int => 'a;

getUnsafe arr i

Unsafe

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

let getUndefined: t('a) => int => Js.undefined('a);

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

let set: t('a) => 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

let setExn: t('a) => int => 'a => unit;

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

let setUnsafe: t('a) => int => 'a => unit;

let shuffleInPlace: t('a) => unit;

shuffleInPlace arr randomly re-orders the items in arr

let shuffle: t('a) => t('a);

shuffle xs

returns a fresh array with items in original array randomly shuffled

let reverseInPlace: t('a) => 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|];;

let reverse: t('a) => t('a);

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|];;

let makeUninitialized: int => array(Js.undefined('a));

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;;

let makeUninitializedUnsafe: int => t('a);

`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");;

let make: int => 'a => t('a);

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

returns an empty array when n is negative.

let range: int => int => t(int);

range start finish create an inclusive array

ocaml

  range 0 3 =  [|0;1;2;3|];;
  range 3 0 =  [||] ;;
  range 3 3 = [|3|];;

let rangeBy: int => int => step:int => t(int);

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|] ;;

let makeByU: int => Js.Fn.arity1((int => 'a)) => t('a);

let makeBy: int => (int => 'a) => t('a);

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|]

let makeByAndShuffleU: int => Js.Fn.arity1((int => 'a)) => t('a);

let makeByAndShuffle: int => (int => 'a) => t('a);

makeByAndShuffle n f

Equivalent to shuffle (makeBy n f)

let zip: t('a) => array('b) => array(('a, 'b));

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)|]

let zipByU: t('a) => array('b) => Js.Fn.arity2(('a => 'b => 'c)) => array('c);

let zipBy: t('a) => array('b) => ('a => 'b => 'c) => array('c);

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|];;

let unzip: array(('a, 'b)) => (t('a), array('b));

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|]);;

let concat: t('a) => t('a) => t('a);

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"|];;

let concatMany: t(t('a)) => t('a);

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|];;

let slice: t('a) => offset:int => len:int => t('a);

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|];;

let sliceToEnd: t('a) => int => t('a);

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|];;

let copy: t('a) => t('a);

copy a

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

let fill: t('a) => 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|];;

let blit: 
  src:t('a) =>
  srcOffset:int =>
  dst:t('a) =>
  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|]

let blitUnsafe: 
  src:t('a) =>
  srcOffset:int =>
  dst:t('a) =>
  dstOffset:int =>
  len:int =>
  unit;

Unsafe blit without bounds checking

let forEachU: t('a) => Js.Fn.arity1(('a => unit)) => unit;

let forEach: t('a) => ('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;;

let mapU: t('a) => Js.Fn.arity1(('a => 'b)) => array('b);

let map: t('a) => ('a => 'b) => array('b);

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|]

let flatMapU: t('a) => Js.Fn.arity1(('a => t('b))) => t('b);

let flatMap: t('a) => ('a => t('b)) => t('b);

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| ```

let getByU: t('a) => Js.Fn.arity1(('a => bool)) => option('a);

let getBy: t('a) => ('a => bool) => option('a);

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

let getIndexByU: t('a) => Js.Fn.arity1(('a => bool)) => option(int);

let getIndexBy: t('a) => ('a => bool) => option(int);

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

let keepU: t('a) => Js.Fn.arity1(('a => bool)) => t('a);

let keep: t('a) => ('a => bool) => t('a);

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|]

let keepWithIndexU: t('a) => Js.Fn.arity2(('a => int => bool)) => t('a);

let keepWithIndex: t('a) => ('a => int => bool) => t('a);

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|]

let keepMapU: t('a) => Js.Fn.arity1(('a => option('b))) => array('b);

let keepMap: t('a) => ('a => option('b)) => array('b);

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 |]

let forEachWithIndexU: t('a) => Js.Fn.arity2((int => 'a => unit)) => unit;

let forEachWithIndex: t('a) => (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;;

let mapWithIndexU: t('a) => Js.Fn.arity2((int => 'a => 'b)) => t('b);

let mapWithIndex: t('a) => (int => 'a => 'b) => t('b);

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|]

let partitionU: t('a) => Js.Fn.arity1(('a => bool)) => (t('a), t('a));

let partition: t('a) => ('a => bool) => (t('a), t('a));

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|]);;

let reduceU: array('b) => 'a => Js.Fn.arity2(('a => 'b => 'a)) => 'a;

let reduce: array('b) => '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";;

let reduceReverseU: array('b) => 'a => Js.Fn.arity2(('a => 'b => 'a)) => 'a;

let reduceReverse: array('b) => '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";;

let reduceReverse2U: 
  t('a) =>
  array('b) =>
  'c =>
  Js.Fn.arity3(('c => 'a => 'b => 'c)) =>
  'c;

let reduceReverse2: t('a) => array('b) => '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

let reduceWithIndexU: 
  t('a) =>
  'b =>
  Js.Fn.arity3(('b => 'a => int => 'b)) =>
  'b;

let reduceWithIndex: t('a) => '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;

let joinWithU: t('a) => string => Js.Fn.arity1(('a => string)) => string;

let joinWith: t('a) => 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"

let someU: t('a) => Js.Fn.arity1(('a => bool)) => bool;

let some: t('a) => ('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;;

let everyU: t('a) => Js.Fn.arity1(('a => bool)) => bool;

let every: t('a) => ('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;;

let every2U: t('a) => t('b) => Js.Fn.arity2(('a => 'b => bool)) => bool;

let every2: t('a) => t('b) => ('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;

let some2U: t('a) => t('b) => Js.Fn.arity2(('a => 'b => bool)) => bool;

let some2: t('a) => t('b) => ('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;;

let cmpU: t('a) => t('a) => Js.Fn.arity2(('a => 'a => int)) => int;

let cmp: t('a) => t('a) => ('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;;

let eqU: t('a) => t('a) => Js.Fn.arity2(('a => 'a => bool)) => bool;

let eq: t('a) => t('a) => ('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

let truncateToLengthUnsafe: t('a) => 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"|];;

let initU: int => Js.Fn.arity1((int => 'a)) => t('a);

let init: int => (int => 'a) => t('a);

let push: t('a) => 'a => unit;

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

Module Belt.Array ​

Module `Belt.Array`