Arrays are mutable data structures with a fixed size, which support fast access and modification, and are used pervasively in imperative computing. While arrays are completely supported in OCaml, it is often a good idea to investigate persistent alternatives, such as lists or hash maps.
A variant of arrays, arrays with capabilities, is provided in module BatArray.Cap. This notion of capabilities permit the transformation of a mutable array into a read-only or a write-only arrays, without loss of speed and with the possibility of distributing different capabilities to different expressions.
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. You can also write a.(n) instead of Array.get a n.
raisesInvalid_argument
if n is outside the range 0 to (Array.length a - 1).
val set : 'a array->int ->'a-> unit
Array.set a n x modifies array a in place, replacing element number n with x. You can also write a.(n) <- x instead of Array.set a n x.
raisesInvalid_argument
if n is outside the range 0 to Array.length a - 1.
val make : 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.
raisesInvalid_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.make_float n returns a fresh float array of length n, with uninitialized data.
since 2.3.0
val of_seq : 'aStdlib.Seq.t->'a array
val to_seq : 'a array->'aStdlib.Seq.t
val to_seqi : 'a array->(int * 'a)Stdlib.Seq.t
val create : int ->'a->'a array
deprecated
Array.create is an alias for Array.make.
val init : int ->(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.
raisesInvalid_argument
if n < 0 or n > Sys.max_array_length. If the return type of f is float, then the maximum size is only Sys.max_array_length / 2.
val make_matrix : int ->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).
raisesInvalid_argument
if dimx or dimy is negative 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.
val create_matrix : int ->int ->'a->'a array array
deprecated
Array.create_matrix is an 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 concatenates a list of arrays.
val sub : 'a array->int ->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.
raisesInvalid_argument
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->int ->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.
raisesInvalid_argument
if ofs and len do not designate a valid subarray of a.
val blit : 'a array->int ->'a array->int ->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.
raisesInvalid_argument
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.
kahan_sum l returns a numerically-accurate sum of the floats of l.
You should consider using Kahan summation when you really care about very small differences in the result, while the result or one of the intermediate sums can be very large (which usually results in loss of precision of floating-point addition).
The worst-case rounding error is constant, instead of growing with (the square root of) the length of the input array as with
fsum. On the other hand, processing each element requires four floating-point operations instead of one. See the wikipedia article on Kahan summation for more details.
tail r pos returns the array containing all but the pos first characters of r
Example: Array.tail [|1;2;3;4;5;6|] 4 = [|5;6|]
val iter : ('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 : ('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 : (int ->'a-> unit)->'a array-> unit
Same as Array.iter, but the function is applied to the index of the element as first argument, and the element itself as second argument.
val mapi : (int ->'a->'b)->'a array->'b array
Same as Array.map, but the function is applied to the index of the element as first argument, and the element itself as second argument.
val fold_left : ('a->'b->'a)->'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.
fold_left_map is a combination of fold_left and map that threads an accumulator through calls to f.
since 3.4.0
Sourceval fold_while :
('acc->'a-> bool)->('acc->'a->'acc)->'acc->'a array->'acc * int
fold_while p f init a, accumulates elements x of array a using function f, as long as the predicate p acc x holds. At the end, the accumulated value along with the first index i where p acc a.(i) does not hold is returned. If the returned index is equal to length a, the whole array was folded.
Array.reduce f a is fold_left f a.(0) [|a.(1); ..; a.(n-1)|]. This is useful for merging a group of things that have no reasonable default value to return if the group is empty.
Create an array consisting of exactly one element.
since 2.1
Sorting
val sort : ('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 (see below for a complete specification). For example, Pervasives.compare is a suitable comparison function, provided there are no floating-point NaN values in the data. After calling Array.sort, the array is sorted in place in increasing order. Array.sort is guaranteed to run in constant heap space and (at most) logarithmic stack space.
The current implementation uses Heap Sort. It runs in constant stack space.
Specification of the comparison function: Let a be the array and cmp the comparison function. The following must be true for all x, y, z in a :
cmp x y > 0 if and only if cmp y x < 0
if cmp x y >= 0 and cmp y z >= 0 then cmp x z >= 0
When Array.sort returns, a contains the same elements as before, reordered in such a way that for all i and j valid indices of a :
cmp a.(i) a.(j) >= 0 if and only if i >= j
val stable_sort : ('a->'a-> int)->'a array-> unit
Same as Array.sort, but the sorting algorithm is stable (i.e. elements that compare equal are kept in their original order) and not guaranteed to run in constant heap space.
The current implementation uses Merge Sort. It uses n/2 words of heap space, where n is the length of the array. It is usually faster than the current implementation of Array.sort.
val fast_sort : ('a->'a-> int)->'a array-> unit
Same as Array.sort or Array.stable_sort, whichever is faster on typical input.
decorate_stable_sort f a returns a sorted copy of a such that if f x < f y then x is earlier in the result than y. This function is useful when f is expensive, as it only computes f x once for each element in the array. See Schwartzian Transform.
It is unnecessary to have an additional comparison function as argument, as the builtin Pervasives.compare is used to compare the 'b values. This is deemed sufficient.
As Array.decorate_stable_sort, but uses fast_sort internally.
Sourceval bsearch :
'aBatOrd.ord->'a array->'a->[ `All_lower | `All_bigger| `Just_after of int| `Empty| `At of int ]
bsearch cmp arr x finds the index of the object x in the array arr, provided arr is sorted using cmp. If the array is not sorted, the result is not specified (may raise Invalid_argument).
Complexity: O(log n) where n is the length of the array (dichotomic search).
returns
`At i if cmp arr.(i) x = 0 (for some i)
`All_lower if all elements of arr are lower than x
`All_bigger if all elements of arr are bigger than x
pivot_split cmp arr x assumes that arr is sorted w.r.t cmp. It splits an array arr of length len into three parts, by returning a couple (i,j) such as:
all elements with indices 0..i-1 (sub arr 0 i) are lower than x
all elements with indices i..j-1 (sub arr i (j-i)) are equal to x
all elements with indices j..len-1 (sub arr j (len-j)) are bigger than x
In particular, it returns:
(0, 0) if all elements of arr are bigger than x
(len, len) if all elements are lower than x
(0, len) if all elements are equal to x
Complexity: logarithmic in the size of the array
raisesInvalid_argument
if the array is found not to be sorted
Operations on two arrays
Sourceval iter2 : ('a->'b-> unit)->'a array->'b array-> unit
Array.iter2 f [|a0; a1; ...; an|] [|b0; b1; ...; bn|] performs calls f a0 b0; f a1 b1; ...; f an bn in that order.
raisesInvalid_argument
if the two arrays have different lengths.
Sourceval iter2i : (int ->'a->'b-> unit)->'a array->'b array-> unit
Array.iter2i f [|a0; a1; ...; an|] [|b0; b1; ...; bn|] performs calls f 0 a0 b0; f 1 a1 b1; ...; f n an bn in that order.
exists p [|a0; a1; ...; an|] checks if at least one element of the array satisfies the predicate p. That is, it returns (p a0) || (p a1) || ... || (p an).
Sourceval partition : ('a-> bool)->'a array->'a array * 'a array
partition p a returns a pair of arrays (a1, a2), where a1 is the array of all the elements of a that satisfy the predicate p, and a2 is the array of all the elements of a that do not satisfy p. The order of the elements in the input array is preserved.
Print the contents of an array, with ~first preceding the first item (default: "[|"), ~last following the last item (default: "|]") and ~sep separating items (default: "; "). A printing function must be provided to print the items in the array.
compare c generates the lexicographical order on arrays induced by c. That is, given a comparison function for the elements of an array, this will return a comparison function for arrays of that type.
Hoist an element comparison function to compare arrays of those elements, with shorter arrays less than longer ones, and lexicographically for arrays of the same size. This is a different ordering than compare, but is often faster.
Sourceval shuffle : ?state:Stdlib.Random.State.t ->'a array-> unit
shuffle ~state:rs a randomly shuffles in place the elements of a. The optional random state rs allows to control the random numbers being used during shuffling (for reproducibility).
Shuffling is implemented using the Fisher-Yates algorithm and works in O(n), where n is the number of elements of a.
Hoist a equality test for elements to arrays. Arrays are only equal if their lengths are the same and corresponding elements test equal.
Override modules
The following modules replace functions defined in Array with functions behaving slightly differently but having the same name. This is by design: the functions are meant to override the corresponding functions of Array.