Array

fromIterator(iterator)

Creates an array from the provided iterator

RES
let map = Map.fromArray([("foo", 1), ("bar", 2)])

Array.fromIterator(map->Map.values) // [1, 2]

make(~length, init)

Creates an array of length length initialized with the value of init.

RES
Array.make(~length=3, #apple) == [#apple, #apple, #apple]

fromInitializer(~length, f)

Creates an array of length length initialized with the value returned from f for each index.

RES
Array.fromInitializer(~length=3, i => i + 3) == [3, 4, 5]

length(array) returns the length of (i.e. number of items in) the array.

See Array.length on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]

Console.log(someArray->Array.length) // 2

fillAll(array, value) fills the entire array with value.

Beware this will mutate the array.

See Array.fill on MDN.

Examples

RESCRIPT
let myArray = [1, 2, 3, 4]
myArray->Array.fillAll(9)

Console.log(myArray) // [9, 9, 9, 9]

fillToEnd(array, value, ~start) fills array with value from the start index.

Beware this will mutate the array.

See Array.fill on MDN.

Examples

RESCRIPT
let myArray = [1, 2, 3, 4]
myArray->Array.fillToEnd(9, ~start=1)

Console.log(myArray) // [1, 9, 9, 9]

fill(array, value, ~start, ~end) fills array with value from start to end.

Beware this will mutate the array.

See Array.fill on MDN.

Examples

RESCRIPT
let myArray = [1, 2, 3, 4]
myArray->Array.fill(9, ~start=1, ~end=2)

Console.log(myArray) // [1, 9, 9, 4]

pop(array) removes the last item from array and returns it.

Beware this will mutate the array.

See Array.pop on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]
let lastItem = someArray->Array.pop // "hello"

Console.log(someArray) // ["hi"]. Notice last item is gone.

push(array, item) appends item to the end of array.

Beware this will mutate the array.

See Array.push on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]
someArray->Array.push("yay")

Console.log(someArray) // ["hi", "hello", "yay"]

pushMany(array, itemsArray) appends many new items to the end of the array.

Beware this will mutate the array.

See Array.push on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]
someArray->Array.pushMany(["yay", "wehoo"])

Console.log(someArray) // ["hi", "hello", "yay", "wehoo"]

reverse(array) reverses the order of the items in array.

Beware this will mutate the array.

See Array.reverse on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]
someArray->Array.reverse

Console.log(someArray) // ["hello", "h1"]

shift(array) removes the first item in the array, and returns it.

Beware this will mutate the array.

See Array.shift on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]
let lastItem = someArray->Array.shift // "hi"

Console.log(someArray) // ["hello"]. Notice first item is gone.

toSorted(array, comparator) returns a new, sorted array from array, using the comparator function.

See Array.toSorted on MDN.

Examples

RESCRIPT
let someArray = [3, 2, 1]
let sorted = someArray->Array.toSorted(Int.compare)

Console.log(sorted) // [1, 2, 3]
Console.log(someArray) // [3, 2, 1]. Original unchanged

sort(array, comparator) sorts array in-place using the comparator function.

Beware this will mutate the array.

See Array.sort on MDN.

Examples

RESCRIPT
let someArray = [3, 2, 1]
someArray->Array.sort((a, b) => float(a - b))

Console.log(someArray) // [1, 2, 3]

unshift(array, item) inserts a new item at the start of the array.

Beware this will mutate the array.

See Array.unshift on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]
someArray->Array.unshift("yay")

Console.log(someArray) // ["yay", "hi", "hello"]

unshiftMany(array, itemsArray) inserts many new items to the start of the array.

Beware this will mutate the array.

See Array.push on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]
someArray->Array.unshiftMany(["yay", "wehoo"])

Console.log(someArray) // ["yay", "wehoo", "hi", "hello"]

concat(array1, array2) concatenates the two arrays, creating a new array.

See Array.concat on MDN.

Examples

RESCRIPT
let array1 = ["hi", "hello"]
let array2 = ["yay", "wehoo"]

let someArray = array1->Array.concat(array2)

Console.log(someArray) // ["hi", "hello", "yay", "wehoo"]

concatMany(array1, arrays) concatenates array1 with several other arrays, creating a new array.

See Array.concat on MDN.

Examples

RESCRIPT
let array1 = ["hi", "hello"]
let array2 = ["yay"]
let array3 = ["wehoo"]

let someArray = array1->Array.concatMany([array2, array3])

Console.log(someArray) // ["hi", "hello", "yay", "wehoo"]

flat(arrays) concatenates an array of arrays into a single array.

See Array.flat on MDN.

Examples

RESCRIPT
Console.log([[1], [2], [3, 4]]->Array.flat) // [1, 2, 3, 4]

includes(array, item) checks whether array includes item, by doing a strict check for equality.

See Array.includes on MDN.

Examples

RESCRIPT
Console.log([1, 2]->Array.includes(1)) // true
Console.log([1, 2]->Array.includes(3)) // false
Console.log([{"language": "ReScript"}]->Array.includes({"language": "ReScript"})) // false, because of strict equality

indexOf(array, item) returns the index of the provided item in array. Uses strict check for equality when comparing items.

Returns -1 if the item doesn not exist. Check out Array.indexOfOpt for a version that returns None instead of -1 if the item does not exist.

See Array.indexOf on MDN.

Examples

RESCRIPT
Console.log([1, 2]->Array.indexOf(2)) // 1
Console.log([1, 2]->Array.indexOf(3)) // -1
Console.log([{"language": "ReScript"}]->Array.indexOf({"language": "ReScript"})) // -1, because of strict equality

indexOfOpt(array, item) returns an option of the index of the provided item in array. Uses strict check for equality when comparing items.

See Array.indexOf on MDN.

Examples

RESCRIPT
Console.log([1, 2]->Array.indexOfOpt(2)) // Some(1)
Console.log([1, 2]->Array.indexOfOpt(3)) // None
Console.log([{"language": "ReScript"}]->Array.indexOfOpt({"language": "ReScript"})) // None, because of strict equality

join(array, separator) produces a string where all items of array are printed, separated by separator. Array items must be strings, to join number or other arrays, use joinUnsafe. Under the hood this will run JavaScript's toString on all the array items.

See Array.join

Examples

RESCRIPT
let array = ["One", "Two", "Three"]

Console.log(array->Array.join(" -- ")) // One -- Two -- Three

joinWith(array, separator) produces a string where all items of array are printed, separated by separator. Array items must be strings, to join number or other arrays, use joinWithUnsafe. Under the hood this will run JavaScript's toString on all the array items.

Examples

RESCRIPT
let array = ["One", "Two", "Three"]

Console.log(array->Array.joinWith(" -- ")) // One -- Two -- Three

joinUnsafe(array, separator) produces a string where all items of array are printed, separated by separator. Under the hood this will run JavaScript's toString on all the array items.

See Array.join

Examples

RESCRIPT
let array = [1, 2, 3]

Console.log(array->Array.joinUnsafe(" -- ")) // 1 -- 2 -- 3

joinWithUnsafe(array, separator) produces a string where all items of array are printed, separated by separator. Under the hood this will run JavaScript's toString on all the array items.

Examples

RESCRIPT
let array = [1, 2, 3]

Console.log(array->Array.joinWithUnsafe(" -- ")) // 1 -- 2 -- 3

slice(array, ~start, ~end) creates a new array of items copied from array from start until (but not including) end.

See Array.slice on MDN.

Examples

RESCRIPT
let myArray = [1, 2, 3, 4]

Console.log(myArray->Array.slice(~start=1, ~end=3)) // [2, 3]

sliceToEnd(array, start) creates a new array from array, with all items from array starting from start.

See Array.slice on MDN.

Examples

RESCRIPT
let myArray = [1, 2, 3, 4]

Console.log(myArray->Array.sliceToEnd(~start=1)) // [2, 3, 4]

copy(array) makes a copy of the array with the items in it, but does not make copies of the items themselves.

Examples

RESCRIPT
let myArray = [1, 2, 3]
let copyOfMyArray = myArray->Array.copy

Console.log(copyOfMyArray) // [1, 2, 3]
Console.log(myArray === copyOfMyArray) // false

toString(array) stringifies array by running toString on all of the array elements and joining them with ",".

See Array.toString on MDN.

Examples

RESCRIPT
let array = [1, 2, 3, 4]

Console.log(array->Array.toString) // "1,2,3,4"

every(array, predicate) returns true if predicate returns true for all items in array.

See Array.every on MDN.

Examples

RESCRIPT
let array = [1, 2, 3, 4]

Console.log(array->Array.every(num => num <= 4)) // true
Console.log(array->Array.every(num => num === 1)) // false

everyWithIndex(array, checker) returns true if all items in array returns true when running the provided checker function.

See Array.every on MDN.

Examples

RESCRIPT
let array = [1, 2, 3, 4]

Console.log(array->Array.everyWithIndex((num, index) => index < 2 && num <= 2)) // true
Console.log(array->Array.everyWithIndex((num, index) => index < 2 && num >= 2)) // false

filter(array, checker) returns a new array containing all elements from array for which the provided checker function returns true.

See Array.filter on MDN.

Examples

RESCRIPT
let array = [1, 2, 3, 4]

Console.log(array->Array.filter(num => num > 2)) // [3, 4]

filterWithIndex(array, checker) returns a new array containing all elements from array for which the provided checker function returns true.

See Array.filter on MDN.

Examples

RESCRIPT
let array = [1, 2, 3, 4]

Console.log(array->Array.filterWithIndex((num, index) => index === 0 || num === 2)) // [1, 2]

find(array, checker) returns the first element of array where the provided checker function returns true.

See Array.find on MDN.

Examples

RESCRIPT
type languages = ReScript | TypeScript | JavaScript

let array = [ReScript, TypeScript, JavaScript]

switch array->Array.find(item => item == ReScript) {
| None => Console.log("No item...")
| Some(_) => Console.log("Yay, ReScript!")
}

findWithIndex(array, checker) returns the first element of array where the provided checker function returns true.

See Array.find on MDN.

Examples

RESCRIPT
type languages = ReScript | TypeScript | JavaScript

let array = [TypeScript, JavaScript, ReScript]

switch array->Array.findWithIndex((item, index) => index > 1 && item == ReScript) {
| None => Console.log("No item...")
| Some(_) => Console.log("Yay, ReScript exists in a later position!")
}

findIndex(array, checker) returns the index of the first element of array where the provided checker function returns true.

Returns -1 if the item does not exist. Consider using Array.findIndexOpt if you want an option instead (where -1 would be None).

See Array.findIndex on MDN.

Examples

RESCRIPT
type languages = ReScript | TypeScript | JavaScript

let array = [ReScript, JavaScript]

Console.log(array->Array.findIndex(item => item == ReScript)) // 0
Console.log(array->Array.findIndex(item => item == TypeScript)) // -1

findIndexWithIndex(array, checker) returns the index of the first element of array where the provided checker function returns true.

Returns -1 if the item does not exist. Consider using Array.findIndexOpt if you want an option instead (where -1 would be None).

See Array.findIndex on MDN.

Examples

RESCRIPT
type languages = ReScript | TypeScript | JavaScript

let array = [ReScript, JavaScript]

let isReScriptFirst = array->Array.findIndexWithIndex((item, index) => index === 0 && item == ReScript)
let isTypeScriptFirst = array->Array.findIndexWithIndex((item, index) => index === 0 && item == TypeScript)

Console.log(isReScriptFirst) // 0
Console.log(isTypeScriptFirst) // -1

forEach(array, fn) runs the provided fn on every element of array.

See Array.forEach on MDN.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]

array->Array.forEach(item => {
  Console.log(item)
})

forEachWithIndex(array, fn) runs the provided fn on every element of array.

See Array.forEach on MDN.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]

array->Array.forEachWithIndex((item, index) => {
  Console.log("At item " ++ Int.toString(index) ++ ": " ++ item)
})

map(array, fn) returns a new array with all elements from array, each element transformed using the provided fn.

See Array.map on MDN.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]
let mappedArray = array->Array.map(greeting => greeting ++ " to you")

Console.log(mappedArray) // ["Hello to you", "Hi to you", "Good bye to you"]

mapWithIndex(array, fn) returns a new array with all elements from array, each element transformed using the provided fn.

See Array.map on MDN.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]
let mappedArray =
  array->Array.mapWithIndex((greeting, index) =>
    greeting ++ " at position " ++ Int.toString(index)
  )

Console.log(mappedArray) // ["Hello at position 0", "Hi at position 1", "Good bye at position 2"]

reduce(xs, init, fn)

Applies fn to each element of xs from beginning to end. Function fn 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
Array.reduce([2, 3, 4], 1, (a, b) => a + b) == 10

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

reduceWithIndex(x, init, fn)

Applies fn to each element of xs from beginning to end. Function fn 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
Array.reduceWithIndex([1, 2, 3, 4], 0, (acc, x, i) => acc + x + i) == 16

reduceRight(xs, init, fn)

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

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

reduceRightWithIndex(xs, init, fn)

Like reduceRight, but with an additional index argument on the callback function.

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

some(array, predicate) returns true if predicate returns true for any element in array.

See Array.some on MDN.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]

Console.log(array->Array.some(greeting => greeting === "Hello")) // true

someWithIndex(array, checker) returns true if running the provided checker function on any element in array returns true.

See Array.some on MDN.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]

Console.log(array->Array.someWithIndex((greeting, index) => greeting === "Hello" && index === 0)) // true

get(array, index) returns the element at index of array.

Returns None if the index does not exist in the array. Equivalent to doing array[index] in JavaScript.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]

array->Array.get(0) == Some("Hello") // true
array->Array.get(3) == None // true

set(array, index, item) sets the provided item at index of array.

Beware this will mutate the array.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]
array->Array.set(1, "Hello")

Console.log(array[1]) // "Hello"

getUnsafe(array, index) returns the element at index of array.

This is unsafe, meaning it will return undefined value if index does not exist in array.

Use Array.getUnsafe only when you are sure the index exists (i.e. when using for-loop).

Examples

RESCRIPT
let array = [1, 2, 3]
for index in 0 to array->Array.length - 1 {
  let value = array->Array.getUnsafe(index)
  Console.log(value)
}

setUnsafe(array, index, item) sets the provided item at index of array.

Beware this will mutate the array, and is unsafe.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]
array->Array.setUnsafe(1, "Hello")

Console.log(array[1]) // "Hello"

findIndexOpt(array, checker) returns the index of the first element of array where the provided checker function returns true.

Returns None if no item matches.

See Array.findIndex on MDN.

Examples

RESCRIPT
type languages = ReScript | TypeScript | JavaScript

let array = [ReScript, TypeScript, JavaScript]

switch array->Array.findIndexOpt(item => item == ReScript) {
| None => Console.log("Ahh, no ReScript...")
| Some(index) => Console.log("Yay, ReScript at index " ++ Int.toString(index))
}

toReversed(array) creates a new array with all items from array in reversed order.

See Array.toReversed on MDN.

Examples

RESCRIPT
let someArray = ["hi", "hello"]
let reversed = someArray->Array.toReversed

Console.log(reversed) // ["hello", "h1"]
Console.log(someArray) // ["h1", "hello"]. Original unchanged

filterMap(array, fn)

Calls fn for each element and returns a new array containing results of the fn calls which are not None.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]

Console.log(
  array->Array.filterMap(item =>
    switch item {
    | "Hello" => Some(item->String.length)
    | _ => None
    }
  ),
) // [5]

keepSome(arr)

Returns a new array containing value for all elements that are Some(value) and ignoring every value that is None

RES
Array.keepSome([Some(1), None, Some(3)]) == [1, 3]

toShuffled(array) returns a new array with all items in array in a random order.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]
let shuffledArray = array->Array.toShuffled

Console.log(shuffledArray)

shuffle(array) randomizes the position of all items in array.

Beware this will mutate the array.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]
array->Array.shuffle

Console.log(array)

flatMap(array, mapper) returns a new array concatenating the arrays returned from running mapper on all items in array.

Examples

RESCRIPT
type language = ReScript | TypeScript | JavaScript

let array = [ReScript, TypeScript, JavaScript]

Console.log(
  array->Array.flatMap(item =>
    switch item {
    | ReScript => [1, 2, 3]
    | TypeScript => [4, 5, 6]
    | JavaScript => [7, 8, 9]
    }
  ),
)
// [1, 2, 3, 4, 5, 6, 7, 8, 9]

flatMapWithIndex(array, mapper) returns a new array concatenating the arrays returned from running mapper on all items in array.

Examples

RESCRIPT
type language = ReScript | TypeScript | JavaScript

let array = [ReScript, TypeScript, JavaScript]

Console.log(
  array->Array.flatMapWithIndex((item, index) =>
    switch item {
    | ReScript => [index]
    | TypeScript => [index, index + 1]
    | JavaScript => [index, index + 1, index + 2]
    }
  ),
)
// [0, 1, 2, 2, 3, 4]

findMap(arr, fn)

Calls fn for each element and returns the first value from fn that is Some(_). Otherwise returns None

RES
Array.findMap([1, 2, 3], n => mod(n, 2) == 0 ? Some(n - 2) : None) == Some(0) // true

at(array, index)

Get an element by its index. Negative indices count backwards from the last item.

Examples

RESCRIPT
["a", "b", "c"]->Array.at(0) // Some("a")
["a", "b", "c"]->Array.at(2) // Some("c")
["a", "b", "c"]->Array.at(3) // None
["a", "b", "c"]->Array.at(-1) // Some("c")
["a", "b", "c"]->Array.at(-3) // Some("a")
["a", "b", "c"]->Array.at(-4) // None

last(array) returns the last element of array.

Returns None if the array is empty.

Examples

RESCRIPT
let array = ["Hello", "Hi", "Good bye"]

array->Array.last == Some("Good bye") // true
[]->Array.last == None // true