An empty array.

Array.empty = [||]

Array.length Array.empty = 0

Create an array with only one element.

Array.singleton 1234 = [|1234|]

Array.singleton "hi" = [|"hi"|]

Return the length of an array.

Array.length [|1; 2, 3|] = 3

Array.length [||] = 0

Determine if an array is empty.

Array.isEmpty Array.empty = true

Array.isEmpty [||] = true

Array.isEmpty [|1; 2; 3|] = false

Initialize an array. Array.initialize ~length:n ~f creates an array of length n with the element at index i initialized to the result of (f i).

Array.initialize ~length:4 ~f:identity = [|0; 1; 2; 3|]

Array.initialize ~length:4 ~f:(fun n -> n * n) = [|0; 1; 4; 9|]

Creates an array of length length with the value x populated at each index.

repeat ~length:5 'a' = [|'a'; 'a'; 'a'; 'a'; 'a'|]

repeat ~length:0 7 = [||]

repeat ~length:(-1) "Why?" = [||]

Creates an array containing all of the integers from from if it is provided or 0 if not, up to but not including to

Array.range 5 = [|0; 1; 2; 3; 4|] 

Array.range ~from: 2 5 = [|2; 3; 4|] 

Array.range ~from:(-2) 3 = [|-2; -1; 0; 1; 2|] 

Create an array from a List.

Array.fromList [1;2;3] = [|1;2;3|]

Create a List of elements from an array.

Array.toList [|1;2;3|] = [1;2;3]

Array.toList (Array.fromList [3; 5; 8]) = [3; 5; 8]

Create an indexed List from an array. Each element of the array will be paired with its index as a Tuple2.

Array.toIndexedList [|"cat"; "dog"|] = [(0, "cat"); (1, "dog")]

Array.get ~index:n a returns, as an Option, the element at index number n of array a.

The first element has index number 0.

The last element has index number Array.length a - 1.

Returns None if n is outside the range 0 to (Array.length a - 1).

You can also write a.(n) instead of Array.get a n but this raises Invalid_argument "index out of bounds" for index outside of the range of the array.

Array.get ~index:2 [|"cat"; "dog"; "eel"|] = Some "eel"

Array.get ~index:5 [|0; 1; 2|] = None

Array.get ~index:0 [||] = None

Array.set a ~index:n ~value:x modifies array a in place, replacing the element at index number n with x.

You can also write a.(n) <- x instead of Array.set a ~index:n ~value:x.

Raises Invalid_argument "index out of bounds" if n is outside the range 0 to Array.length a - 1.

    let setZero = Array.set ~value:0 in
let numbers = [|1;2;3|] in
  
setZero numbers ~index:2;
setZero numbers ~index:1;

numbers = [|1;0;0|]

    let setZerothElement = Array.set ~index:0 in
let animals = [|"ant"; "bat"; "cat"|] in

setZerothElement animals ~value:"antelope";

animals = [|"antelope"; "bat"; "cat"|]

Get the total of adding all of the integers in an array.

Array.sum [|1; 2; 3|] = 6

Get the total of adding all of the floating point numbers in an array.

Array.floatSum [|1.0; 2.0; 3.0|] = 6.0

Keep elements that f returns true for.

Array.filter ~f:Int.isEven [|1; 2; 3; 4; 5; 6|] = [|2; 4; 6|]

Create a new array which is the result of applying a function f to every element.

Array.map ~f:sqrt [|1.0; 4.0; 9.0|] = [|1.0; 2.0; 3.0|]

Apply a function f to every element with its index as the first argument.

Array.mapWithIndex ~f:( * ) [|5; 5; 5|] = [|0; 5; 10|]

Combine two arrays, using f to combine each pair of elements. If one array is longer, the extra elements are dropped.

    let totals (xs : int array) (ys : int array) : int array =
Array.map2 ~f:(+) xs ys in

totals [|1;2;3|] [|4;5;6|] = [|5;7;9|]
  
Array.map2 
  ~f:Tuple2.create 
  [|"alice"; "bob"; "chuck"|] 
  [|2; 5; 7; 8|] = 
    [|("alice",2); ("bob",5); ("chuck",7)|] 

Combine three arrays, using f to combine each Tuple3 of elements. If one array is longer, the extra elements are dropped.

Array.map3 
  ~f:Tuple3.create 
  [|"alice"; "bob"; "chuck"|] 
  [|2; 5; 7; 8;|] 
  [|true; false; true; false|] = 
    [|("alice", 2, true); ("bob", 5, false); ("chuck", 7, true)|]

Apply a function f onto an array and flatten the resulting array of arrays.

Array.flatMap ~f xs = Array.map ~f xs |> Array.flatten

Array.flatMap ~f:(fun n -> [|n; n|]) [|1; 2; 3|] = [|1; 1; 2; 2; 3; 3|]

Returns as an option the first element for which f evaluates to true. If f doesn't return true for any of the elements find will return None

Array.find ~f:Int.isEven [|1; 3; 4; 8;|] = Some 4

Array.find ~f:Int.isOdd [|0; 2; 4; 8;|] = None

Array.find ~f:Int.isEven [||] = None

Determine if f returns true for any values in an array.

Array.any ~f:isEven [|2;3|] = true

Array.any ~f:isEven [|1;3|] = false

Array.any ~f:isEven [||] = false

Determine if f returns true for all values in an array.

Array.all ~f:Int.isEven [|2;4|] = true

Array.all ~f:Int.isEven [|2;3|] = false

Array.all ~f:Int.isEven [||] = true

Creates a new array which is the result of appending the second array onto the end of the first.

    let fortyTwos = Array.repeat ~length:2 42 in 
let eightyOnes = Array.repeat ~length:3 81 in
Array.append fourtyTwos eightyOnes = [|42; 42; 81; 81; 81|];

Concatenate an array of arrays into a single array:

Array.concatenate [|[|1; 2|]; [|3|]; [|4; 5|]|] = [|1; 2; 3; 4; 5|]

Places sep between all elements of the given array.

Array.intersperse ~sep:"on" [|"turtles"; "turtles"; "turtles"|] = [|"turtles"; "on"; "turtles"; "on"; "turtles"|]

Array.intersperse ~sep:0 [||] = [||]

Get a sub-section of an array. from is a zero-based index where we will start our slice. The to_ is a zero-based index that indicates the end of the slice.

The slice extracts up to but not including to_.

Array.slice ~from:0  ~to_:3 [|0; 1; 2; 3; 4|] = [|0; 1; 2|]

Array.slice ~from:1  ~to_:4 [|0; 1; 2; 3; 4|] = [|1; 2; 3|]

Array.slice ~from:5  ~to_:3 [|0; 1; 2; 3; 4|] = [||]

Both the from and to_ indexes can be negative, indicating an offset from the end of the array.

Array.slice  ~from:1 ~to_:(-1) [|0; 1; 2; 3; 4|] = [|1; 2; 3|]

Array.slice ~from:(-2)  ~to_:5 [|0; 1; 2; 3; 4|] = [|3; 4|]

Array.slice ~from:(-2)  ~to_:(-1) [|0; 1; 2; 3; 4|] = [|3|]

Reduces collection to a value which is the accumulated result of running each element in the array through f, where each successive invocation is supplied the return value of the previous.

Read foldLeft as 'fold from the left'.

Array.foldLeft ~f:( * ) ~initial:1 (Array.repeat ~length:4 7) = 2401

Array.foldLeft ~f:((fun element list -> element :: list)) ~initial:[] [|1; 2; 3|] = [3; 2; 1]

This method is like foldLeft except that it iterates over the elements of the array from right to left.

Array.foldRight ~f:(+) ~initial:0 (Array.repeat ~length:3 5) = 15

Array.foldRight ~f:(fun element list -> element :: list) ~initial:[] [|1; 2; 3|] = [1; 2; 3]

Create a new reversed array leaving the original untouched

  let numbers = [|1; 2; 3|] in
Array.reverse numbers = [|3; 2; 1|];
numbers = [|1; 2; 3|]; 

Reverses array so that the first element becomes the last, the second element becomes the second to last, and so on.

  let numbers = [|1; 2; 3|] in
Array.reverseInPlace numbers;
numbers = [|3; 2; 1|]

Iterates over the elements of invokes f for each element.

Array.forEach [|1; 2; 3|] ~f:(fun int -> print (Int.toString int))