19.2 Module Array: array operations

```val length : 'a array -> int
```
Return the length (number of elements) of the given array.
```val get: 'a array -> int -> 'a
```
`Array.get a n` returns the element number `n` of array `a`. The first element has number 0. The last element has number `Array.length a - 1`. Raise `Invalid_argument "Array.get"` if `n` is outside the range 0 to `(Array.length a - 1)`. You can also write `a.(n)` instead of `Array.get a n`.
```val set: 'a array -> int -> 'a -> unit
```
`Array.set a n x` modifies array `a` in place, replacing element number `n` with `x`. Raise `Invalid_argument "Array.set"` if `n` is outside the range 0 to `Array.length a - 1`. You can also write `a.(n) <- x` instead of `Array.set a n x`.
```val make: int -> 'a -> 'a array
val create: int -> 'a -> 'a array
```
`Array.make n x` returns a fresh array of length `n`, initialized with `x`. All the elements of this new array are initially physically equal to `x` (in the sense of the `==` predicate). Consequently, if `x` is mutable, it is shared among all elements of the array, and modifying `x` through one of the array entries will modify all other entries at the same time. Raise `Invalid_argument` if `n <= 0` or `n > Sys.max_array_length`. If the value of `x` is a floating-point number, then the maximum size is only `Sys.max_array_length / 2`. `Array.create` is a deprecated alias for `Array.make`.
```val init: int -> f:(int -> 'a) -> 'a array
```
`Array.init n f` returns a fresh array of length `n`, with element number `i` initialized to the result of `f i`. In other terms, `Array.init n f` tabulates the results of `f` applied to the integers `0` to `n-1`.
```val make_matrix: dimx:int -> dimy:int -> 'a -> 'a array array
val create_matrix: dimx:int -> dimy:int -> 'a -> 'a array array
```
`Array.make_matrix dimx dimy e` returns a two-dimensional array (an array of arrays) with first dimension `dimx` and second dimension `dimy`. All the elements of this new matrix are initially physically equal to `e`. The element (`x,y`) of a matrix `m` is accessed with the notation `m.(x).(y)`. Raise `Invalid_argument` if `dimx` or `dimy` is less than 1 or greater than `Sys.max_array_length`. If the value of `e` is a floating-point number, then the maximum size is only `Sys.max_array_length / 2`. `Array.create_matrix` is a deprecated alias for `Array.make_matrix`.
```val append: 'a array -> 'a array -> 'a array
```
`Array.append v1 v2` returns a fresh array containing the concatenation of the arrays `v1` and `v2`.
```val concat: 'a array list -> 'a array
```
Same as `Array.append`, but catenates a list of arrays.
```val sub: 'a array -> pos:int -> len:int -> 'a array
```
`Array.sub a start len` returns a fresh array of length `len`, containing the elements number `start` to `start + len - 1` of array `a`. Raise `Invalid_argument "Array.sub"` if `start` and `len` do not designate a valid subarray of `a`; that is, if `start < 0`, or `len < 0`, or `start + len > Array.length a`.
```val copy: 'a array -> 'a array
```
`Array.copy a` returns a copy of `a`, that is, a fresh array containing the same elements as `a`.
```val fill: 'a array -> pos:int -> len:int -> 'a -> unit
```
`Array.fill a ofs len x` modifies the array `a` in place, storing `x` in elements number `ofs` to `ofs + len - 1`. Raise `Invalid_argument "Array.fill"` if `ofs` and `len` do not designate a valid subarray of `a`.
```val blit: src:'a array -> src_pos:int ->
dst:'a array -> dst_pos:int -> len:int -> unit
```
`Array.blit v1 o1 v2 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. Raise `Invalid_argument "Array.blit"` if `o1` and `len` do not designate a valid subarray of `v1`, or if `o2` and `len` do not designate a valid subarray of `v2`.
```val to_list: 'a array -> 'a list
```
`Array.to_list a` returns the list of all the elements of `a`.
```val of_list: 'a list -> 'a array
```
`Array.of_list l` returns a fresh array containing the elements of `l`.
```val iter: f:('a -> unit) -> 'a array -> unit
```
`Array.iter f a` applies function `f` in turn to all the elements of `a`. It is equivalent to `f a.(0); f a.(1); ...; f a.(Array.length a - 1); ()`.
```val map: f:('a -> 'b) -> 'a array -> 'b array
```
`Array.map f a` applies function `f` to all the elements of `a`, and builds an array with the results returned by `f`: `[| f a.(0); f a.(1); ...; f a.(Array.length a - 1) |]`.
```val iteri: f:(int -> 'a -> unit) -> 'a array -> unit
val mapi: f:(int -> 'a -> 'b) -> 'a array -> 'b array
```
Same as `Array.iter` and `Array.map` respectively, but the function is applied to the index of the element as first argument, and the element itself as second argument.
```val fold_left: f:('a -> 'b -> 'a) -> init:'a -> 'b array -> 'a
```
`Array.fold_left f x a` computes `f (... (f (f x a.(0)) a.(1)) ...) a.(n-1)`, where `n` is the length of the array `a`.
```val fold_right: f:('b -> 'a -> 'a) -> 'b array -> init:'a -> 'a
```
`Array.fold_right f a x` computes `f a.(0) (f a.(1) ( ... (f a.(n-1) x) ...))`, where `n` is the length of the array `a`.
 Sorting
```val sort : cmp:('a -> 'a -> int) -> 'a array -> unit;;
```
Sort an array in increasing order according to a comparison function. The comparison function must return 0 if its arguments compare as equal, a positive integer if the first is greater, and a negative integer if the first is smaller. For example, the `compare` function is a suitable comparison function. After calling `Array.sort`, the array is sorted in place in increasing order. `Array.sort` is guaranteed to run in constant heap space and logarithmic stack space.

The current implementation uses Heap Sort. It runs in constant stack space.
```val stable_sort : cmp:('a -> 'a -> int) -> 'a array -> unit;;
```
Same as `Array.sort`, but the sorting algorithm is stable and not guaranteed to use a fixed amount of heap memory. The current implementation is Merge Sort. It uses `n/2` words of heap space, where `n` is the length of the array. It is faster than the current implementation of `Array.sort`.