package reason-standard

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A mutable, fixed length collection of elements which must have the same type.

Has constant time (O(1)) get, set and length operations.

Since arrays have a fixed length, if you want to be able to add an arbitrary number of elements maybe you want a List.

A fixed lenfth collection of values

type 'a t = 'a array

Create

You can create an array in OCaml with the [|1; 2; 3|] syntax.

val singleton : 'a -> 'a t

Create an array with only one element.

Examples

Array.singleton 1234 = [|1234|]
Array.singleton "hi" = [|"hi"|]
val repeat : 'a -> length:int -> 'a t

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

Examples

Array.repeat ~length:5 'a' = [|'a'; 'a'; 'a'; 'a'; 'a'|]
Array.repeat ~length:0 7 = [||]
Array.repeat ~length:(-1) "Why?" = [||]
val range : ?from:int -> int -> int t

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

Examples

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|]
val initialize : int -> f:(int -> 'a) -> 'a t

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

Examples

Array.initialize 4 ~f:identity = [|0; 1; 2; 3|]
Array.initialize 4 ~f:(fun n -> n * n) = [|0; 1; 4; 9|]
val ofList : 'a list -> 'a t

Create an array from a List.

Examples

Array.ofList [1;2;3] = [|1;2;3|]
val clone : 'a t -> 'a t

Create a shallow copy of an array.

Examples

let numbers = [|1;2;3|] in
let otherNumbers = Array.copy numbers in
numbers.(1) <- 9;
numbers = [|1;9;3|];
otherNumbers = [|1;2;3|];
let numberGrid = [|
  [|1;2;3|];
  [|4;5;6|];
  [|7;8;9|];
|] in

let numberGridCopy = Array.copy numberGrid in

numberGridCopy.(1).(1) = 5;
numberGrid.(1).(1) <- 0;        
numberGridCopy.(1).(1) = 0;

Basic operations

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

Get the element at the specified index.

The first element has index number 0.

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

You should prefer using the dedicated literal syntax;

array.(n)

Or using the safer Array.getAt function.

Exceptions

Raises Invalid_argument "index out of bounds" for indexes outside of the range 0 to (Array.length a - 1).

Examples

[|1; 2; 3; 2; 1|].(3) = 2
let animals = [|"cat"; "dog"; "eel"|] in
animals.(2) = "eel"
val getAt : 'a t -> index:int -> 'a option

Returns, as an Option, the element at index number n of array a.

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

Examples

Array.getAt [|0; 1; 2|] ~index:5 = None
Array.getAt [||] ~index:0 = None
val (.?()) : 'element array -> int -> 'element option

The index operator version of getAt

Note Currently this is only supported by the OCaml syntax.

Examples

Array.([||].?(3)) = Some 'g'
Array.([||].?(9)) = None
val set : 'a t -> int -> 'a -> unit

Modifies an array in place, replacing the element at index with value.

You should prefer either to write

array.(index) <- value

Or use the setAt function instead.

Exceptions

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

Examples

let numbers = [|1;2;3|] in
Array.set numbers 1 1;
numbers.(2) <- 0;

numbers = [|1;0;0|]
val setAt : 'a t -> index:int -> value:'a -> unit

Like set but with labelled arguments

val first : 'a t -> 'a option

Get the first element of an array.

Returns None if the array is empty.

Examples

Array.first [1;2;3] = Some 1
Array.first [1] = Some 1
Array.first [] = None
val last : 'a t -> 'a option

Get the last element of an array.

Returns None if the array is empty.

Examples

Array.last [1;2;3] = Some 3
Array.last [1] = Some 1
Array.last [] = None
val slice : ?to_:int -> 'a t -> from:int -> 'a t

Get a sub-section of a list. 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_.

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

Examples

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] = []
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]
val swap : 'a t -> int -> int -> unit

Swaps the values at the provided indicies.

Exceptions

Raises an Invalid_argument exception of either index is out of bounds for the array.

Examples

Array.swap [|1; 2; 3|] 1 2 = [|1; 3; 2|]
val reverse : 'a t -> unit

Reverses an array in place, mutating the existing array.

Examples

let numbers = [|1; 2; 3|] in
Array.reverse numbers
numbers = [|3; 2; 1|];
val sort : 'a t -> compare:('a -> 'a -> int) -> unit

Sort in place, modifying the existing array, using the provided compare function to determine order.

On native it uses merge sort which means the sort is stable, runs in constant heap space, logarithmic stack space and n * log (n) time.

When targeting javascript the time and space complexity of the sort cannot be guaranteed as it depends on the implementation.

Examples

Array.sortInPlace [|5;6;8;3;6|] ~compare:compare = [|3;5;6;6;8|]

Query

val isEmpty : 'a t -> bool

Check if an array is empty

Examples

Array.isEmpty [|1; 2; 3|] = false
Array.isEmpty [||] = true
val length : 'a t -> int

Return the length of an array.

Examples

Array.length [|1; 2; 3|] = 3
Array.length [||] = 0
val any : 'a t -> f:('a -> bool) -> bool

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

Iteration is stopped as soon as f returns true

Examples

Array.any ~f:Int.isEven [|1;2;3;5|] = true
Array.any ~f:Int.isEven [|1;3;5;7|] = false
Array.any ~f:Int.isEven [||] = false
val all : 'a t -> f:('a -> bool) -> bool

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

Iteration is stopped as soon as f returns false

Examples

Array.all ~f:Int.isEven [|2;4|] = true
Array.all ~f:Int.isEven [|2;3|] = false
Array.all ~f:Int.isEven [||] = true
val count : 'a t -> f:('a -> bool) -> int

Count the number of elements which f returns true for

Examples

Array.count [|7; 5; 8; 6|] ~f:Int.isEven = 2
val find : 'a t -> f:('a -> bool) -> 'a option

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

Examples

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
val findIndex : 'a t -> f:(int -> 'a -> bool) -> (int * 'a) option

Similar to Array.find but f is also called with the current index, and the return value will be a tuple of the index the passing value was found at and the passing value.

Examples

Array.findIndex [|1; 3; 4; 8;|] ~f:(fun index number -> index > 2 && Int.isEven number) = Some (3, 8)
val includes : 'a t -> 'a -> equal:('a -> 'a -> bool) -> bool

Test if an array contains the specified element using the provided equal to test for equality.

Examples

Array.includes [|1; 2; 3|] 2 ~equal:Int.equal = true
val minimum : 'a t -> compare:('a -> 'a -> int) -> 'a option

Find the smallest element using the provided compare function.

Returns None if called on an empty array.

Examples

Array.minimum [|7;5;8;6|] ~compare:Int.compare = Some 5
Array.minimum [||] ~compare:Int.compare = None
val maximum : 'a t -> compare:('a -> 'a -> int) -> 'a option

Find the largest element using the provided compare function.

Returns None if called on an empty array.

Examples

Array.maximum [|7;5;8;6|] ~compare:Int.compare = Some 8
Array.maximum [||] ~compare:Int.compare = None
val extent : 'a t -> compare:('a -> 'a -> int) -> ('a * 'a) option

Find a Tuple of the minimum and maximum in a single pass

Returns None if called on an empty array.

Examples

Array.extent [|7;5;8;6|] ~compare:Int.compare = Some (5, 8)
Array.extent [|7|] ~compare:Int.compare = Some (7, 7)
Array.extent [||] ~compare:Int.compare = None
val sum : 'a t -> (module Standard__.Core.Container.Sum with type t = 'a) -> 'a

Calculate the sum of a list using the provided modules zero value and add function.

Examples

Array.sum [|1; 2; 3|] (module Int) = 6
Array.sum [|4.0; 4.5; 5.0|] (module Float) = 13.5
Array.sum 
  [|"a"; "b"; "c"|] 
  (
    module struct
      type t = string
      let zero = ""
      let add = (^)
    end
  ) 
  = "abc"

Transform

val map : 'a t -> f:('a -> 'b) -> 'b t

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

Examples

Array.map ~f:Float.squareRoot [|1.0; 4.0; 9.0|] = [|1.0; 2.0; 3.0|]
val mapI : 'a t -> f:(int -> 'a -> 'b) -> 'b t

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

Examples

Array.mapWithIndex ~f:( * ) [|5; 5; 5|] = [|0; 5; 10|]
val filter : 'a t -> f:('a -> bool) -> 'a t

Keep elements that f returns true for.

Examples

Array.filter ~f:Int.isEven [|1; 2; 3; 4; 5; 6|] = [|2; 4; 6|]
val filterMap : 'a t -> f:('a -> 'b option) -> 'b t

Allows you to combine map and filter into a single pass.

The output array only contains elements for which f returns Some.

Why filterMap and not just filter then map?

filterMap removes the Option layer automatically.

If your mapping is already returning an Option and you want to skip over Nones, then filterMap is much nicer to use.

Examples

let characters = [|'a'; '9'; '6'; ' '; '2'; 'z' |] in
Array.filterMap characters ~f:Char.toDigit = [|9; 6; 2|]
Array.filterMap [|3; 4; 5; 6|] ~f:(fun number ->
  if Int.isEven number then
    Some (number * number)
  else
    None
) = [16; 36]
val flatMap : 'a t -> f:('a -> 'b t) -> 'b t

map f onto an array and flatten the resulting arrays

Examples

Array.flatMap ~f:(fun n -> [|n; n|]) [|1; 2; 3|] = [|1; 1; 2; 2; 3; 3|]
val fold : 'a t -> initial:'b -> f:('b -> 'a -> 'b) -> 'b

Produce a new value from an array.

fold takes two arguments, an initial 'accumulator' value and a function f.

For each element of the array f will be called with two arguments; the current accumulator and an element.

f returns the value that the accumulator should have for the next iteration.

The initial value is the value the accumulator will have on the first call to f.

After applying f to every element of the array, fold returns the accumulator.

fold iterates over the elements of the array from first to last.

Folding is useful whenever you have a collection of something, and want to produce a single value from it.

For examples if we have:

let numbers = [|1, 2; 3|] in
let sum =
  Array.fold numbers ~initial:0 ~f:(fun accumulator element -> accumulator +element)
in
sum = 6

Walking though each iteration step by step:

  1. accumulator: 0, element: 1, result: 1
  2. accumulator: 1, element: 2, result: 3
  3. accumulator: 3, element: 3, result: 6

And so the final result is 6. (Note that in reality you probably want to use Array.sum)

Examples

Array.fold [|1; 2; 3|] ~initial:[] ~f:(List.cons) = [3; 2; 1]
Array.fold [|1; 1; 2; 2; 3|] ~initial:Set.Int.empty ~f:Set.add |> Set.toArray = [|1; 2; 3|]
let lastEven integers =
  Array.fold integers ~initial:None ~f:(fun last int ->
    if Int.isEven then
      Some int
    else
      last
  )
in
lastEven [|1;2;3;4;5|] = Some 4
val foldRight : 'a t -> initial:'b -> f:('b -> 'a -> 'b) -> 'b

This method is like fold except that it iterates over the elements of the array from last to first.

Examples

Array.foldRight ~f:(+) ~initial:0 (Array.repeat ~length:3 5) = 15
Array.foldRight ~f:List.cons ~initial:[] [|1; 2; 3|] = [1; 2; 3]

Combine

val append : 'a t -> 'a t -> 'a t

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

Examples

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|];
val flatten : 'a t t -> 'a t

Concatenate an array of arrays into a single array:

Examples

Array.flatten [|[|1; 2|]; [|3|]; [|4; 5|]|] = [|1; 2; 3; 4; 5|]
val zip : 'a t -> 'b t -> ('a * 'b) t

Combine two arrays by merging each pair of elements into a Tuple

If one array is longer, the extra elements are dropped.

The same as Array.map2 ~f:Tuple.make

Examples

Array.zip [|1;2;3;4;5|] [|"Dog"; "Eagle"; "Ferret"|] = [|(1, "Dog"); (2, "Eagle"); (3, "Ferret")|]
val map2 : 'a t -> 'b t -> f:('a -> 'b -> 'c) -> 'c t

Combine two arrays, using f to combine each pair of elements.

If one array is longer, the extra elements are dropped.

Examples

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:Tuple.create
  [|"alice"; "bob"; "chuck"|]
  [|2; 5; 7; 8|] =
    [|("alice",2); ("bob",5); ("chuck",7)|]
val map3 : 'a t -> 'b t -> 'c t -> f:('a -> 'b -> 'c -> 'd) -> 'd t

Combine three arrays, using f to combine each trio of elements.

If one array is longer, the extra elements are dropped.

Examples

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)|]

Deconstruct

val partition : 'a t -> f:('a -> bool) -> 'a t * 'a t

Split an array into a Tuple of arrays. Values which f returns true for will end up in Tuple.first.

Examples

Array.partition [|1;2;3;4;5;6|] ~f:Int.isOdd = ([|1;3;5|], [|2;4;6|])
val splitAt : 'a t -> index:int -> 'a t * 'a t

Divides an array into a Tuple of arrays.

Elements which have index upto (but not including) index will be in the first component of the tuple.

Elements with an index greater than or equal to index will be in the second.

Exceptions

Raises an Invalid_argument exception if index is less than zero

Examples

Array.splitAt [|1;2;3;4;5|] ~index:2 = ([|1;2|], [|3;4;5|])
Array.splitAt [|1;2;3;4;5|] ~index:10 = ([|1;2;3;4;5|], [||])
Array.splitAt [|1;2;3;4;5|] ~index:0 = ([||], [|1;2;3;4;5|])
val splitWhen : 'a t -> f:('a -> bool) -> 'a t * 'a t

Divides an array at the first element f returns true for.

Returns a Tuple, the first component contains the elements f returned false for, the second component includes the element that f retutned true for an all the remaining elements.

Examples

Array.splitWhen 
  [|5; 7; 8; 6; 4;|]
  ~f:Int.isEven = 
  ([|5; 7|], [|8; 6; 4|])
Array.splitWhen 
  [|"Ant"; "Bat"; "Cat"|] 
  ~f:(fun animal -> String.length animal > 3) =
    ([|"Ant"; "Bat"; "Cat"|], [||])
Array.splitWhen [|2.; Float.pi; 1.111|] ~f:Float.isInteger =
  ([||], [|2.; Float.pi; 1.111|])
val unzip : ('a * 'b) t -> 'a t * 'b t

Decompose an array of Tuples into a Tuple of arrays.

Examples

Array.unzip [(0, true); (17, false); (1337, true)] = ([0;17;1337], [true; false; true])

Iterate

val forEach : 'a t -> f:('a -> unit) -> unit

Iterates over the elements of invokes f for each element.

Examples

Array.forEach [|1; 2; 3|] ~f:(fun int -> print (Int.toString int))
val forEachI : 'a t -> f:(int -> 'a -> unit) -> unit

Iterates over the elements of invokes f for each element.

Examples

Array.forEachI [|1; 2; 3|] ~f:(fun index int -> printf "%d: %d" index int)
(*
  0: 1
  1: 2
  2: 3
*)
val values : 'a option t -> 'a t

Return all of the Some values from an array of options

Examples

Array.values [|(Some "Ant"); None; (Some "Cat")|] = [|"Ant"; "Cat"|]
Array.values [|None; None; None|] = [||]
val intersperse : 'a t -> sep:'a -> 'a t

Places sep between all the elements of the given array.

Examples

Array.intersperse ~sep:"on" [|"turtles"; "turtles"; "turtles"|] =
[|"turtles"; "on"; "turtles"; "on"; "turtles"|]
Array.intersperse ~sep:0 [||] = [||]
val chunksOf : 'a t -> size:int -> 'a t t

Split an array into equally sized chunks.

If there aren't enough elements to make the last 'chunk', those elements are ignored.

Examples

Array.chunksOf ~size:2 [|"#FFBA49"; "#9984D4"; "#20A39E"; "#EF5B5B"; "#23001E"|] =  [|
  [|"#FFBA49"; "#9984D4"|];
  [|"#20A39E"; "#EF5B5B"|];
|]
val sliding : ?step:int -> 'a t -> size:int -> 'a t t

Provides a sliding 'window' of sub-arrays over an array.

The first sub-array starts at index 0 of the array and takes the first size elements.

The sub-array then advances the index step (which defaults to 1) positions before taking the next size elements.

The sub-arrays are guaranteed to always be of length size and iteration stops once a sub-array would extend beyond the end of the array.

Examples

Array.sliding [|1;2;3;4;5|] ~size:1 = [|[|1|]; [|2|]; [|3|]; [|4|]; [|5|]|] 
Array.sliding [|1;2;3;4;5|] ~size:2 = [|[|1;2|]; [|2;3|]; [|3;4|]; [|4;5|]|] 
Array.sliding [|1;2;3;4;5|] ~size:3 = [|[|1;2;3|]; [|2;3;4|]; [|3;4;5|]|] 
Array.sliding [|1;2;3;4;5|] ~size:2 ~step:2 = [|[|1;2|]; [|3;4|]|] 
Array.sliding [|1;2;3;4;5|] ~size:1 ~step:3 = [|[|1|]; [|4|]|]

Convert

val join : string t -> sep:string -> string

Converts a list of strings into a String, placing sep between each string in the result.

Examples

Array.join [|"Ant"; "Bat"; "Cat"|] ~sep:", " = "Ant, Bat, Cat"
val groupBy : 'value t -> (module Standard__.Core.Comparator.S with type identity = 'id and type t = 'key) -> f:('value -> 'key) -> ('key, 'value list, 'id) Standard__.Core.Map.t

Collect elements which f produces the same key for

Produces a map from 'key to a List of all elements which produce the same 'key

Examples

let animals = [|"Ant"; "Bear"; "Cat"; "Dewgong"|] in
Array.groupBy animals (module Int) ~f:String.length = Map.Int.ofList [
  (3, ["Cat"; "Ant"]);
  (4, ["Bear"]);
  (7, ["Dewgong"]);
]
val toList : 'a t -> 'a list

Create a List of elements from an array.

Examples

Array.toList [|1;2;3|] = [1;2;3]
Array.toList (Array.ofList [3; 5; 8]) = [3; 5; 8]
val toIndexedList : 'a t -> (int * 'a) list

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

Examples

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

Compare

val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool

Test two arrays for equality using the provided function to test pairs of elements.

val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int

Compare two arrays using the provided function to compare pairs of elements.

A shorter array is 'less' than a longer one.

Examples

Array.compare Int.compare [|1;2;3|] [|1;2;3;4|] = -1
Array.compare Int.compare [|1;2;3|] [|1;2;3|] = 0
Array.compare Int.compare [|1;2;5|] [|1;2;3|] = 1