API / Belt / Array

Array

Utililites for Array functions.

Note about index syntax

Code like arr[0] does not compile to JavaScript arr[0]. ReScript transforms the [] index syntax into a function: Array.get(arr, 0). By default, this uses the default standard library's Array.get function, which may raise an exception if the index isn't found. If you open Belt, it will use the Belt.Array.get function which returns options instead of raising exceptions. See this for more information.

length

RES
let length: array<'a> => int

return the size of the array

RES
// Returns 1
Belt.Array.length(["test"])

size

RES
let size: array<'a> => int

See Belt_Array.length

get

RES
let get: (array<'a>, int) => option<'a>

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

getExn

RES
let getExn: (array<'a>, int) => 'a

Raise an exception if i is out of range. Otherwise return the value at index i in arr.

getUnsafe

RES
let getUnsafe: (array<'a>, int) => 'a

Unsafe

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

getUndefined

RES
let getUndefined: (array<'a>, int) => Js.undefined<'a>

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

set

RES
let set: (array<'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.

setExn

RES
let setExn: (array<'a>, int, 'a) => unit

setExn(arr, i, x) raise an exception if i is out of range.

setUnsafe

RES
let setUnsafe: (array<'a>, int, 'a) => unit

shuffleInPlace

RES
let shuffleInPlace: array<'a> => unit

shuffleInPlace(arr) randomly re-orders the items in arr

shuffle

RES
let shuffle: array<'a> => array<'a>

Returns a fresh array with items in original array randomly shuffled.

reverseInPlace

RES
let reverseInPlace: array<'a> => unit

reverseInPlace(arr) reverses items in arr in place.

RES
let arr = [10, 11, 12, 13, 14]

let () = Belt.Array.reverseInPlace(arr)

arr == [14, 13, 12, 11, 10]

reverse

RES
let reverse: array<'a> => array<'a>

reverse(arr) returns a fresh array with items in arr in reverse order.

RES
Belt.Array.reverse([10, 11, 12, 13, 14]) == [14, 13, 12, 11, 10]

makeUninitialized

RES
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.

RES
let arr: array<Js.undefined<string>> = Belt.Array.makeUninitialized(5)

Belt.Array.getExn(arr, 0) == Js.undefined

makeUninitializedUnsafe

RES
let makeUninitializedUnsafe: int => array<'a>

Unsafe

RES
let arr = Belt.Array.makeUninitializedUnsafe(5)

Js.log(Belt.Array.getExn(arr, 0)) // undefined

Belt.Array.setExn(arr, 0, "example")

Js.log(Belt.Array.getExn(arr, 0) == "example")

make

RES
let make: (int, 'a) => array<'a>

make(n, e) return an array of size n filled with value e. Returns an empty array when n is negative.

range

RES
let range: (int, int) => array<int>

range(start, finish) create an inclusive array.

RES
Belt.Array.range(0, 3) == [0, 1, 2, 3]

Belt.Array.range(3, 0) == []

Belt.Array.range(3, 3) == [3]

rangeBy

RES
let rangeBy: (int, int, ~step: int) => array<int>

rangeBy(start, finish, ~step)

Returns empty array when step is 0 or negative. It also return an empty array when start > finish.

RES
Belt.Array.rangeBy(0, 10, ~step=3) == [0, 3, 6, 9]

Belt.Array.rangeBy(0, 12, ~step=3) == [0, 3, 6, 9, 12]

Belt.Array.rangeBy(33, 0, ~step=1) == []

Belt.Array.rangeBy(33, 0, ~step=-1) == []

Belt.Array.rangeBy(3, 12, ~step=-1) == []

Belt.Array.rangeBy(3, 3, ~step=0) == []

Belt.Array.rangeBy(3, 3, ~step=1) == [3]

makeByU

RES
let makeByU: (int, (. int) => 'a) => array<'a>

makeBy

RES
let makeBy: (int, int => 'a) => array<'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.

RES
Belt.Array.makeBy(5, (i) => i) == [0, 1, 2, 3, 4]

Belt.Array.makeBy(5, (i) => i * i) == [0, 1, 4, 9, 16]

makeByAndShuffleU

RES
let makeByAndShuffleU: (int, (. int) => 'a) => array<'a>

makeByAndShuffle

RES
let makeByAndShuffle: (int, int => 'a) => array<'a>

makeByAndShuffle(n, f)

Equivalent to shuffle(makeBy(n, f))

zip

RES
let zip: (array<'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.

RES
Belt.Array.zip([1, 2], [3, 4, 5]) == [(1, 3), (2, 4)]

zipByU

RES
let zipByU: (array<'a>, array<'b>, (. 'a, 'b) => 'c) => array<'c>

zipBy

RES
let zipBy: (array<'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), ((a, b)) => f(a, b))

RES
Belt.Array.zipBy([1, 2, 3], [4, 5], (a, b) => 2 * a + b) == [6, 9]

unzip

RES
let unzip: array<('a, 'b)> => (array<'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.

RES
Belt.Array.unzip([(1, 2), (3, 4)]) == ([1, 3], [2, 4])

Belt.Array.unzip([(1, 2), (3, 4), (5, 6), (7, 8)]) == ([1, 3, 5, 7], [2, 4, 6, 8])

concat

RES
let concat: (array<'a>, array<'a>) => array<'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

RES
Belt.Array.concat([1, 2, 3], [4, 5]) == [1, 2, 3, 4, 5]

Belt.Array.concat([], ["a", "b", "c"]) == ["a", "b", "c"]

concatMany

RES
let concatMany: array<array<'a>> => array<'a>

concatMany(xss)

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

RES
Belt.Array.concatMany([[1, 2, 3], [4, 5, 6], [7, 8]]) == [1, 2, 3, 4, 5, 6, 7, 8]

slice

RES
let slice: (array<'a>, ~offset: int, ~len: int) => array<'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.

RES
Belt.Array.slice([10, 11, 12, 13, 14, 15, 16], ~offset=2, ~len=3) == [12, 13, 14]

Belt.Array.slice([10, 11, 12, 13, 14, 15, 16], ~offset=-4, ~len=3) == [13, 14, 15]

Belt.Array.slice([10, 11, 12, 13, 14, 15, 16], ~offset=4, ~len=9) == [14, 15, 16]

sliceToEnd

RES
let sliceToEnd: (array<'a>, int) => array<'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

RES
Belt.Array.sliceToEnd([10, 11, 12, 13, 14, 15, 16], 2) == [12, 13, 14, 15, 16]

Belt.Array.sliceToEnd([10, 11, 12, 13, 14, 15, 16], -4) == [13, 14, 15, 16]

copy

RES
let copy: array<'a> => array<'a>

copy(a)

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

fill

RES
let fill: (array<'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

RES
let arr = Belt.Array.makeBy(5, (i) => i)

Belt.Array.fill(arr, ~offset=2, ~len=2, 9)

arr == [0, 1, 9, 9, 4]

Belt.Array.fill(arr, ~offset=7, ~len=2, 8)

arr == [0, 1, 9, 9, 4]

blit

RES
let blit:
  (
    ~src: array<'a>,
    ~srcOffset: int,
    ~dst: array<'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.

RES
let v1 = [10, 11, 12, 13, 14, 15, 16, 17]
let v2 = [20, 21, 22, 23, 24, 25, 26, 27]

Belt.Array.blit(~src=v1, ~srcOffset=4, ~dst=v2, ~dstOffset=2, ~len=3)
v2 == [20, 21, 14, 15, 16, 25, 26, 27]

Belt.Array.blit(~src=v1, ~srcOffset=4, ~dst=v1, ~dstOffset=2, ~len=3)
v1 == [10, 11, 14, 15, 16, 15, 16, 17]

blitUnsafe

RES
let blitUnsafe: (~src: array<'a>, ~srcOffset: int, ~dst: array<'a>, ~dstOffset: int, ~len: int) => unit

Unsafe blit without bounds checking.

forEachU

RES
let forEachU: (array<'a>, (. 'a) => unit) => unit

forEach

RES
let forEach: (array<'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.

RES
Belt.Array.forEach(["a", "b", "c"], x => Js.log("Item: " ++ x))

/*
  prints:
  Item: a
  Item: b
  Item: c
*/
let total = ref(0)

Belt.Array.forEach([1, 2, 3, 4], x => total := total.contents + x)

total.contents == 1 + 2 + 3 + 4

mapU

RES
let mapU: (array<'a>, (. 'a) => 'b) => array<'b>

map

RES
let map: (array<'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.

RES
Belt.Array.map([1, 2], (x) => x + 1) == [3, 4]

getByU

RES
let getByU: (array<'a>, (. 'a) => bool) => option<'a>

getBy

RES
let getBy: (array<'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.

RES
Belt.Array.getBy([1, 4, 3, 2], (x) => mod(x, 2) == 0) == Some(4)
Belt.Array.getBy([15, 13, 11], (x) => mod(x, 2) == 0) == None

getIndexByU

RES
let getIndexByU: (array<'a>, (. 'a) => bool) => option<int>

getIndexBy

RES
let getIndexBy: (array<'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.

RES
Belt.Array.getIndexBy([1, 4, 3, 2], (x) => mod(x, 2) == 0) == Some(1)
Belt.Array.getIndexBy([15, 13, 11], (x) => mod(x, 2) == 0) == None

keepU

RES
let keepU: (array<'a>, (. 'a) => bool) => array<'a>

keep

RES
let keep: (array<'a>, 'a => bool) => array<'a>

keep(xs, p)

Returns a new array that keep all elements satisfy p.

RES
Belt.Array.keep([1, 2, 3], (x) => mod(x, 2) == 0) == [2]

keepWithIndexU

RES
let keepWithIndexU: (array<'a>, (. 'a, int) => bool) => array<'a>

keepWithIndex

RES
let keepWithIndex: (array<'a>, ('a, int) => bool) => array<'a>

keepWithIndex(xs, p)

Returns a new array that keep all elements satisfy p.

RES
Belt.Array.keepWithIndex([1, 2, 3], (_x, i) => i == 1) == [2]

keepMapU

RES
let keepMapU: (array<'a>, (. 'a) => option<'b>) => array<'b>

keepMap

RES
let keepMap: (array<'a>, 'a => option<'b>) => array<'b>

keepMap(xs, p)

Returns a new array that keep all elements that return a non-None applied p.

RES
Belt.Array.keepMap([1, 2, 3], x =>
  if mod(x, 2) == 0 {
    Some(x)
  } else {
    None
  }
)
== [2]

forEachWithIndexU

RES
let forEachWithIndexU: (array<'a>, (. int, 'a) => unit) => unit

forEachWithIndex

RES
let forEachWithIndex: (array<'a>, (int, 'a) => unit) => unit

forEachWithIndex(xs, f)

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

RES
Belt.Array.forEachWithIndex(["a", "b", "c"], (i, x) => Js.log("Item " ++ Belt.Int.toString(i) ++ " is " ++ x))

/*
  prints:
  Item 0 is a
  Item 1 is b
  Item 2 is cc
*/
let total = ref(0)

Belt.Array.forEachWithIndex([10, 11, 12, 13], (i, x) => total := total.contents + x + i)

total.contents == 0 + 10 + 1 + 11 + 2 + 12 + 3 + 13

mapWithIndexU

RES
let mapWithIndexU: (array<'a>, (. int, 'a) => 'b) => array<'b>

mapWithIndex

RES
let mapWithIndex: (array<'a>, (int, 'a) => 'b) => array<'b>

mapWithIndex(xs, f)

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.

RES
Belt.Array.mapWithIndex([1, 2, 3], (i, x) => i + x) == [0 + 1, 1 + 2, 2 + 3]

partitionU

RES
let partitionU: (array<'a>, (. 'a) => bool) => (array<'a>, array<'a>)

partition

RES
let partition: (array<'a>, 'a => bool) => (array<'a>, array<'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

RES
Belt.Array.partition([1, 2, 3, 4, 5], (x) => mod(x, 2) == 0) == ([2, 4], [1, 3, 5])

Belt.Array.partition([1, 2, 3, 4, 5], (x) => mod(x, 2) != 0) == ([1, 3, 5], [2, 4])

reduceU

RES
let reduceU: (array<'b>, 'a, (. 'a, 'b) => 'a) => 'a

reduce

RES
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.

RES
Belt.Array.reduce([2, 3, 4], 1, (a, b) => a + b) == 10

Belt.Array.reduce(["a", "b", "c", "d"], "", (a, b) => a ++ b) == "abcd"

reduceReverseU

RES
let reduceReverseU: (array<'b>, 'a, (. 'a, 'b) => 'a) => 'a

reduceReverse

RES
let reduceReverse: (array<'b>, 'a, ('a, 'b) => 'a) => 'a

reduceReverse(xs, init, f)

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

RES
Belt.Array.reduceReverse(["a", "b", "c", "d"], "", (a, b) => a ++ b) == "dcba"

reduceReverse2U

RES
let reduceReverse2U: (array<'a>, array<'b>, 'c, (. 'c, 'a, 'b) => 'c) => 'c

reduceReverse2

RES
let reduceReverse2: (array<'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.

RES
Belt.Array.reduceReverse2([1, 2, 3], [1, 2], 0, (acc, x, y) => acc + x + y) == 6

reduceWithIndexU

RES
let reduceWithIndexU: (array<'a>, 'b, (. 'b, 'a, int) => 'b) => 'b

reduceWithIndex

RES
let reduceWithIndex: (array<'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.

RES
Belt.Array.reduceWithIndex([1, 2, 3, 4], 0, (acc, x, i) => acc + x + i) == 16

someU

RES
let someU: (array<'a>, (. 'a) => bool) => bool

some

RES
let some: (array<'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.

RES
Belt.Array.some([2, 3, 4], (x) => mod(x, 2) == 1) == true

Belt.Array.some([(-1), (-3), (-5)], (x) => x > 0) == false

everyU

RES
let everyU: (array<'a>, (. 'a) => bool) => bool

every

RES
let every: (array<'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.

RES
Belt.Array.every([1, 3, 5], (x) => mod(x, 2) == 1) == true

Belt.Array.every([1, (-3), 5], (x) => x > 0) == false

every2U

RES
let every2U: (array<'a>, array<'b>, (. 'a, 'b) => bool) => bool

every2

RES
let every2: (array<'a>, array<'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)))

RES
Belt.Array.every2([1, 2, 3], [0, 1], (a, b) => a > b) == true

Belt.Array.every2([], [1], (x, y) => x > y) == true

Belt.Array.every2([2, 3], [1], (x, y) => x > y) == true

Belt.Array.every2([0, 1], [5, 0], (x, y) => x > y) == false

some2U

RES
let some2U: (array<'a>, array<'b>, (. 'a, 'b) => bool) => bool

some2

RES
let some2: (array<'a>, array<'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)))

RES
Belt.Array.some2([0, 2], [1, 0, 3], (a, b) => a > b) == true

Belt.Array.some2([], [1], (x, y) => x > y) == false

Belt.Array.some2([2, 3], [1, 4], (x, y) => x > y) == true

cmpU

RES
let cmpU: (array<'a>, array<'a>, (. 'a, 'a) => int) => int

cmp

RES
let cmp: (array<'a>, array<'a>, ('a, 'a) => int) => int

cmp(xs, ys, f)

Compared by length if length(xs) != length(ys); returning -1 if length(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.

RES
Belt.Array.cmp([1, 3, 5], [1, 4, 2], (a, b) => compare(a, b)) == -1

Belt.Array.cmp([1, 3, 5], [1, 2, 3], (a, b) => compare(a, b)) == 1

Belt.Array.cmp([1, 3, 5], [1, 3, 5], (a, b) => compare(a, b)) == 0

eqU

RES
let eqU: (array<'a>, array<'a>, (. 'a, 'a) => bool) => bool

eq

RES
let eq: (array<'a>, array<'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 truefalse otherwise

RES
Belt.Array.eq([1, 2, 3], [(-1), (-2), (-3)], (a, b) => abs(a) == abs(b)) == true

truncateToLengthUnsafe

RES
let truncateToLengthUnsafe: (array<'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.

RES
let arr = ["ant", "bee", "cat", "dog", "elk"]

Belt.Array.truncateToLengthUnsafe(arr, 3)

arr == ["ant", "bee", "cat"]