Provided by: ocaml-man_5.3.0-2_all 
NAME
Array - Array operations.
Module
Module Array
Documentation
Module Array
: sig end
Array operations.
The labeled version of this module can be used as described in the StdLabels module.
type 'a t = 'a array
An alias for the type of arrays.
val length : 'a array -> int
Return the length (number of elements) of the given array.
val get : 'a array -> int -> 'a
get a n returns the element number n of array a . The first element has number 0. The last element has
number length a - 1 . You can also write a.(n) instead of get a n .
Raises Invalid_argument if n is outside the range 0 to (length a - 1) .
val set : 'a array -> int -> 'a -> unit
set a n x modifies array a in place, replacing element number n with x . You can also write a.(n) <- x
instead of set a n x .
Raises Invalid_argument if n is outside the range 0 to length a - 1 .
val make : int -> 'a -> 'a 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.
Raises 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 .
val create_float : int -> float array
create_float n returns a fresh float array of length n , with uninitialized data.
Since 4.03
val init : int -> (int -> 'a) -> 'a 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, init n f tabulates the results of f applied in order to the integers 0 to n-1 .
Raises Invalid_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
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) .
Raises Invalid_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 init_matrix : int -> int -> (int -> int -> 'a) -> 'a array array
init_matrix dimx dimy f returns a two-dimensional array (an array of arrays) with first dimension dimx
and second dimension dimy , where the element at index ( x,y ) is initialized with f x y . The element (
x,y ) of a matrix m is accessed with the notation m.(x).(y) .
Since 5.2
Raises Invalid_argument if dimx or dimy is negative or greater than Sys.max_array_length . If the return
type of f is float , then the maximum size is only Sys.max_array_length / 2 .
val append : 'a array -> 'a array -> 'a array
append v1 v2 returns a fresh array containing the concatenation of the arrays v1 and v2 .
Raises Invalid_argument if length v1 + length v2 > Sys.max_array_length .
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
sub a pos len returns a fresh array of length len , containing the elements number pos to pos + len - 1
of array a .
Raises Invalid_argument if pos and len do not designate a valid subarray of a ; that is, if pos < 0 , or
len < 0 , or pos + len > length a .
val copy : 'a array -> 'a 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
fill a pos len x modifies the array a in place, storing x in elements number pos to pos + len - 1 .
Raises Invalid_argument if pos and len do not designate a valid subarray of a .
val blit : 'a array -> int -> 'a array -> int -> int -> unit
blit src src_pos dst dst_pos len copies len elements from array src , starting at element number src_pos
, to array dst , starting at element number dst_pos . It works correctly even if src and dst are the same
array, and the source and destination chunks overlap.
Raises Invalid_argument if src_pos and len do not designate a valid subarray of src , or if dst_pos and
len do not designate a valid subarray of dst .
val to_list : 'a array -> 'a list
to_list a returns the list of all the elements of a .
val of_list : 'a list -> 'a array
of_list l returns a fresh array containing the elements of l .
Raises Invalid_argument if the length of l is greater than Sys.max_array_length .
Iterators
val iter : ('a -> unit) -> 'a array -> unit
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.(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 map : ('a -> 'b) -> 'a array -> 'b 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.(length a - 1) |] .
val map_inplace : ('a -> 'a) -> 'a array -> unit
map_inplace f a applies function f to all elements of a , and updates their values in place.
Since 5.1
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 mapi_inplace : (int -> 'a -> 'a) -> 'a array -> unit
Same as Array.map_inplace , but the function is applied to the index of the element as first argument,
and the element itself as second argument.
Since 5.1
val fold_left : ('acc -> 'a -> 'acc) -> 'acc -> 'a array -> 'acc
fold_left f init a computes f (... (f (f init a.(0)) a.(1)) ...) a.(n-1) , where n is the length of the
array a .
val fold_left_map : ('acc -> 'a -> 'acc * 'b) -> 'acc -> 'a array -> 'acc * 'b array
fold_left_map is a combination of Array.fold_left and Array.map that threads an accumulator through calls
to f .
Since 4.13
val fold_right : ('a -> 'acc -> 'acc) -> 'a array -> 'acc -> 'acc
fold_right f a init computes f a.(0) (f a.(1) ( ... (f a.(n-1) init) ...)) , where n is the length of
the array a .
Iterators on two arrays
val iter2 : ('a -> 'b -> unit) -> 'a array -> 'b array -> unit
iter2 f a b applies function f to all the elements of a and b .
Since 4.03 (4.05 in ArrayLabels)
Raises Invalid_argument if the arrays are not the same size.
val map2 : ('a -> 'b -> 'c) -> 'a array -> 'b array -> 'c array
map2 f a b applies function f to all the elements of a and b , and builds an array with the results
returned by f : [| f a.(0) b.(0); ...; f a.(length a - 1) b.(length b - 1)|] .
Since 4.03 (4.05 in ArrayLabels)
Raises Invalid_argument if the arrays are not the same size.
Array scanning
val for_all : ('a -> bool) -> 'a array -> bool
for_all f [|a1; ...; an|] checks if all elements of the array satisfy the predicate f . That is, it
returns (f a1) && (f a2) && ... && (f an) .
Since 4.03
val exists : ('a -> bool) -> 'a array -> bool
exists f [|a1; ...; an|] checks if at least one element of the array satisfies the predicate f . That is,
it returns (f a1) || (f a2) || ... || (f an) .
Since 4.03
val for_all2 : ('a -> 'b -> bool) -> 'a array -> 'b array -> bool
Same as Array.for_all , but for a two-argument predicate.
Since 4.11
Raises Invalid_argument if the two arrays have different lengths.
val exists2 : ('a -> 'b -> bool) -> 'a array -> 'b array -> bool
Same as Array.exists , but for a two-argument predicate.
Since 4.11
Raises Invalid_argument if the two arrays have different lengths.
val mem : 'a -> 'a array -> bool
mem a set is true if and only if a is structurally equal to an element of set (i.e. there is an x in set
such that compare a x = 0 ).
Since 4.03
val memq : 'a -> 'a array -> bool
Same as Array.mem , but uses physical equality instead of structural equality to compare array elements.
Since 4.03
val find_opt : ('a -> bool) -> 'a array -> 'a option
find_opt f a returns the first element of the array a that satisfies the predicate f , or None if there
is no value that satisfies f in the array a .
Since 4.13
val find_index : ('a -> bool) -> 'a array -> int option
find_index f a returns Some i , where i is the index of the first element of the array a that satisfies f
x , if there is such an element.
It returns None if there is no such element.
Since 5.1
val find_map : ('a -> 'b option) -> 'a array -> 'b option
find_map f a applies f to the elements of a in order, and returns the first result of the form Some v ,
or None if none exist.
Since 4.13
val find_mapi : (int -> 'a -> 'b option) -> 'a array -> 'b option
Same as find_map , but the predicate is applied to the index of the element as first argument (counting
from 0), and the element itself as second argument.
Since 5.1
Arrays of pairs
val split : ('a * 'b) array -> 'a array * 'b array
split [|(a1,b1); ...; (an,bn)|] is ([|a1; ...; an|], [|b1; ...; bn|]) .
Since 4.13
val combine : 'a array -> 'b array -> ('a * 'b) array
combine [|a1; ...; an|] [|b1; ...; bn|] is [|(a1,b1); ...; (an,bn)|] . Raise Invalid_argument if the two
arrays have different lengths.
Since 4.13
Sorting and shuffling
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, compare is a
suitable comparison function. After calling sort , the array is sorted in place in increasing order.
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 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 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 a temporary array of length n/2 , 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.
val shuffle : rand:(int -> int) -> 'a array -> unit
shuffle rand a randomly permutes a 's element using rand for randomness. The distribution of permutations
is uniform.
rand must be such that a call to rand n returns a uniformly distributed random number in the range [ 0 ;
n-1 ]. Random.int can be used for this (do not forget to Random.self_init the generator).
Since 5.2
Arrays and Sequences
val to_seq : 'a array -> 'a Seq.t
Iterate on the array, in increasing order. Modifications of the array during iteration will be reflected
in the sequence.
Since 4.07
val to_seqi : 'a array -> (int * 'a) Seq.t
Iterate on the array, in increasing order, yielding indices along elements. Modifications of the array
during iteration will be reflected in the sequence.
Since 4.07
val of_seq : 'a Seq.t -> 'a array
Create an array from the generator
Since 4.07
Arrays and concurrency safety
Care must be taken when concurrently accessing arrays from multiple domains: accessing an array will
never crash a program, but unsynchronized accesses might yield surprising (non-sequentially-consistent)
results.
Atomicity
Every array operation that accesses more than one array element is not atomic. This includes iteration,
scanning, sorting, splitting and combining arrays.
For example, consider the following program:
let size = 100_000_000
let a = Array.make size 1
let d1 = Domain.spawn (fun () ->
Array.iteri (fun i x -> a.(i) <- x + 1) a
)
let d2 = Domain.spawn (fun () ->
Array.iteri (fun i x -> a.(i) <- 2 * x + 1) a
)
let () = Domain.join d1; Domain.join d2
After executing this code, each field of the array a is either 2 , 3 , 4 or 5 . If atomicity is required,
then the user must implement their own synchronization (for example, using Mutex.t ).
Data races
If two domains only access disjoint parts of the array, then the observed behaviour is the equivalent to
some sequential interleaving of the operations from the two domains.
A data race is said to occur when two domains access the same array element without synchronization and
at least one of the accesses is a write. In the absence of data races, the observed behaviour is
equivalent to some sequential interleaving of the operations from different domains.
Whenever possible, data races should be avoided by using synchronization to mediate the accesses to the
array elements.
Indeed, in the presence of data races, programs will not crash but the observed behaviour may not be
equivalent to any sequential interleaving of operations from different domains. Nevertheless, even in the
presence of data races, a read operation will return the value of some prior write to that location (with
a few exceptions for float arrays).
Float arrays
Float arrays have two supplementary caveats in the presence of data races.
First, the blit operation might copy an array byte-by-byte. Data races between such a blit operation and
another operation might produce surprising values due to tearing: partial writes interleaved with other
operations can create float values that would not exist with a sequential execution.
For instance, at the end of
let zeros = Array.make size 0.
let max_floats = Array.make size Float.max_float
let res = Array.copy zeros
let d1 = Domain.spawn (fun () -> Array.blit zeros 0 res 0 size)
let d2 = Domain.spawn (fun () -> Array.blit max_floats 0 res 0 size)
let () = Domain.join d1; Domain.join d2
the res array might contain values that are neither 0. nor max_float .
Second, on 32-bit architectures, getting or setting a field involves two separate memory accesses. In the
presence of data races, the user may observe tearing on any operation.