Module Belt_Array

length xs return the size of the array

See length

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

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;;

getExn arr i

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

getUnsafe arr i

Unsafe

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

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

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

shuffleInPlace arr randomly re-orders the items in arr

shuffle xs

• returns

  a fresh array with items in original array randomly shuffled

reverseInPlace arr reverses items in arr in place

let arr = [|10;11;12;13;14|];;
let () = reverseInPlace arr;;
arr = [|14;13;12;11;10|];;

reverse arr

• returns

  a fresh array with items in arr in reverse order

  reverse [|10;11;12;13;14|] = [|14;13;12;11;10|];;

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.

let arr: string Js.undefined array = makeUninitialized 5;;
getExn arr 0 = Js.undefined;;

`makeUninitializedUnsafe n`

Unsafe

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");;

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

• returns

  an empty array when n is negative.

range start finish create an inclusive array

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

rangeBy start finish ~step

• returns

  empty array when step is 0 or negative it also return empty array when start > finish

  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|] ;;

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

makeBy 5 (fun i -> i) = [|0;1;2;3;4|];;
makeBy 5 (fun i -> i * i) = [|0;1;4;9;16|]

makeByAndShuffle n f

Equivalent to shuffle (makeBy n f)

zip a b

Create an array of pairs from corresponding elements of a and b. Stop with the shorter array

zip [|1;2|] [|3;4;5|] = [|(1, 3);(2, 4)|]

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)

zipBy [|1;2;3|] [|4;5|] (fun a b -> 2 * a + b) = [|6;9|];;

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.

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|]);;

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

  concat [|1;2;3|] [|4;5|] = [|1;2;3;4;5|];;
  concat [| |] [|"a";"b";"c"|] = [|"a";"b";"c"|];;

concatMany xss

• returns

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

  concatMany [| [|1;2;3|]; [|4;5;6|]; [|7;8|] |] = [|1;2;3;4;5;6;7;8|];;

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.

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|];;

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

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|];;

copy a

• returns

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

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

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|];;

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.

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|]

Unsafe blit without bounds checking

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.

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;;

map xs f

• returns

  a new array by calling f for each element of xs from the beginning to end

  map [|1;2|] (fun x-> x + 10) = [|11;12|]

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| ```

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.

getBy [|1;4;3;2|] (fun x -> x mod 2 = 0) = Some 4
getBy [|15;13;11|] (fun x -> x mod 2 = 0) = None

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.

getIndexBy [|1;4;3;2|] (fun x -> x mod 2 = 0) = Some 1
getIndexBy [|15;13;11|] (fun x -> x mod 2 = 0) = None

keep xs p

• returns

  a new array that keeps all elements satisfying p

  keep [|1;2;3|] (fun x -> x mod  2 = 0) = [|2|]

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.

  keepWithIndex [|1;2;3|] (fun _x i -> i = 1) = [|2|]

keepMap xs p

• returns

  a new array that keeps all elements that return a non-None when applied to p

  keepMap [|1;2;3|] (fun x -> if x mod 2 = 0 then Some x else None)
  = [| 2 |]

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

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;;

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.

mapWithIndex [|1;2;3|] (fun i x -> i + x) =
[|0 + 1; 1 + 2; 2 + 3|]

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

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|]);;

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.

reduce [|2;3;4|] 1 (+) = 10;;
reduce [|"a";"b";"c";"d"|] "" (^) = "abcd";;

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.

reduceReverse [|"a";"b";"c";"d"|] "" (^) = "dcba";;

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.

reduceReverse2 [|1;2;3|] [|1;2|] 0 (fun acc x y -> acc + x + y) = 6

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.

reduceWithIndex [|1;2;3;4|] 0 (fun acc x i -> acc + x + i) = 16;

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.

joinWith [|0; 1|] ", " string_of_int = "0, 1"
joinWith [||] " " string_of_int = ""
joinWith [|1|] " " string_of_int = "1"

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.

  some [|2; 3; 4|] (fun x -> x mod 2 = 1) = true;;
  some [|-1; -3; -5|] (fun x -> x > 0) = false;;

every xs p

• returns

  true if all elements satisfy p;where p is a predicate: a function taking an element and returning a bool.

  every [|1; 3; 5|] (fun x -> x mod 2 = 1) = true;;
  every [|1; -3; 5|] (fun x -> x > 0) = false;;

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))

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;

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))

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;;

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.

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;;

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

eq [|1; 2; 3|] [|-1; -2; -3|] (fun a b -> abs a = abs b) = true

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.

let arr = [|"ant";"bee";"cat";"dog";"elk"|];;
let () = truncateToLengthUnsafe arr 3;;
arr = [|"ant";"bee";"cat"|];;

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