Array
Utililites for Array functions.
Note about index syntax
Code like arr[0] does not compile to JavaScript arr[0]. Reason transforms the [] index syntax into a function: Array.get(arr, 0). By default, this uses the default standard library's Array.get function, which may raise an exception if the index isn't found. If you open Belt, it will use the Belt.Array.get function which returns options instead of raising exceptions. See this for more information.
length
let length: array<'a> => int
return the size of the array
RES// Returns 1
Belt.Array.length(["test"])
size
let size: array<'a> => int
See Belt_Array.length
get
let get: (array<'a>, int) => option<'a>
If i <= 0 <= length(arr) returns Some(value) where value is the item at index i.
If i is out of range returns None
getExn
let getExn: (array<'a>, int) => 'a
Raise an exception if i is out of range.
Otherwise return the value at index i in arr.
getUnsafe
let getUnsafe: (array<'a>, int) => 'a
Unsafe
no bounds checking; this would cause type error if i does not stay within range
getUndefined
let getUndefined: (array<'a>, int) => Js.undefined<'a>
It does the samething in the runtime as Belt_Array.getUnsafe it is type safe since the return type still track whether it is in range or not
set
let set: (array<'a>, int, 'a) => bool
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
let setExn: (array<'a>, int, 'a) => unit
setExn(arr, i, x) raise an exception if i is out of range.
setUnsafe
let setUnsafe: (array<'a>, int, 'a) => unit
shuffleInPlace
let shuffleInPlace: array<'a> => unit
shuffleInPlace(arr) randomly re-orders the items in arr
shuffle
let shuffle: array<'a> => array<'a>
Returns a fresh array with items in original array randomly shuffled.
reverseInPlace
let reverseInPlace: array<'a> => unit
reverseInPlace(arr) reverses items in arr in place.
RESlet arr = [10, 11, 12, 13, 14]
let () = Belt.Array.reverseInPlace(arr)
arr == [14, 13, 12, 11, 10]
reverse
let reverse: array<'a> => array<'a>
reverse(arr) returns a fresh array with items in arr in reverse order.
RESBelt.Array.reverse([10, 11, 12, 13, 14]) == [14, 13, 12, 11, 10]
makeUninitialized
let makeUninitialized: int => array<Js.undefined<'a>>
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.
RESlet arr: array<Js.undefined<string>> = Belt.Array.makeUninitialized(5)
Belt.Array.getExn(arr, 0) == Js.undefined
makeUninitializedUnsafe
let makeUninitializedUnsafe: int => array<'a>
Unsafe
RESlet arr = Belt.Array.makeUninitializedUnsafe(5)
Js.log(Belt.Array.getExn(arr, 0)) // undefined
Belt.Array.setExn(arr, 0, "example")
Js.log(Belt.Array.getExn(arr, 0) == "example")
make
let make: (int, 'a) => array<'a>
make(n, e) return an array of size n filled with value e.
Returns an empty array when n is negative.
range
let range: (int, int) => array<int>
range(start, finish) create an inclusive array.
RESBelt.Array.range(0, 3) == [0, 1, 2, 3]
Belt.Array.range(3, 0) == []
Belt.Array.range(3, 3) == [3]
rangeBy
let rangeBy: (int, int, ~step: int) => array<int>
rangeBy(start, finish, ~step)
Returns empty array when step is 0 or negative. It also return an empty array when start > finish.
RESBelt.Array.rangeBy(0, 10, ~step=3) == [0, 3, 6, 9]
Belt.Array.rangeBy(0, 12, ~step=3) == [0, 3, 6, 9, 12]
Belt.Array.rangeBy(33, 0, ~step=1) == []
Belt.Array.rangeBy(33, 0, ~step=-1) == []
Belt.Array.rangeBy(3, 12, ~step=-1) == []
Belt.Array.rangeBy(3, 3, ~step=0) == []
Belt.Array.rangeBy(3, 3, ~step=1) == [3]
makeByU
let makeByU: (int, (. int) => 'a) => array<'a>
makeBy
let makeBy: (int, int => 'a) => array<'a>
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.
RESBelt.Array.makeBy(5, (i) => i) == [0, 1, 2, 3, 4]
Belt.Array.makeBy(5, (i) => i * i) == [0, 1, 4, 9, 16]
makeByAndShuffleU
let makeByAndShuffleU: (int, (. int) => 'a) => array<'a>
makeByAndShuffle
let makeByAndShuffle: (int, int => 'a) => array<'a>
makeByAndShuffle(n, f)
Equivalent to shuffle(makeBy(n, f))
zip
let zip: (array<'a>, array<'b>) => array<('a, 'b)>
zip(a, b)
Create an array of pairs from corresponding elements of a and b. Stop with the shorter array.
RESBelt.Array.zip([1, 2], [3, 4, 5]) == [(1, 3), (2, 4)]
zipByU
let zipByU: (array<'a>, array<'b>, (. 'a, 'b) => 'c) => array<'c>
zipBy
let zipBy: (array<'a>, array<'b>, ('a, 'b) => 'c) => array<'c>
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), ((a, b)) => f(a, b))
RESBelt.Array.zipBy([1, 2, 3], [4, 5], (a, b) => 2 * a + b) == [6, 9]
unzip
let unzip: array<('a, 'b)> => (array<'a>, array<'b>)
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.
RESBelt.Array.unzip([(1, 2), (3, 4)]) == ([1, 3], [2, 4])
Belt.Array.unzip([(1, 2), (3, 4), (5, 6), (7, 8)]) == ([1, 3, 5, 7], [2, 4, 6, 8])
concat
let concat: (array<'a>, array<'a>) => array<'a>
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
RESBelt.Array.concat([1, 2, 3], [4, 5]) == [1, 2, 3, 4, 5]
Belt.Array.concat([], ["a", "b", "c"]) == ["a", "b", "c"]
concatMany
let concatMany: array<array<'a>> => array<'a>
concatMany(xss)
Returns a fresh array as the concatenation of xss (an array of arrays)
RESBelt.Array.concatMany([[1, 2, 3], [4, 5, 6], [7, 8]]) == [1, 2, 3, 4, 5, 6, 7, 8]
slice
let slice: (array<'a>, ~offset: int, ~len: int) => array<'a>
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.
RESBelt.Array.slice([10, 11, 12, 13, 14, 15, 16], ~offset=2, ~len=3) == [12, 13, 14]
Belt.Array.slice([10, 11, 12, 13, 14, 15, 16], ~offset=-4, ~len=3) == [13, 14, 15]
Belt.Array.slice([10, 11, 12, 13, 14, 15, 16], ~offset=4, ~len=9) == [14, 15, 16]
sliceToEnd
let sliceToEnd: (array<'a>, int) => array<'a>
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
RESBelt.Array.sliceToEnd([10, 11, 12, 13, 14, 15, 16], 2) == [12, 13, 14, 15, 16]
Belt.Array.sliceToEnd([10, 11, 12, 13, 14, 15, 16], -4) == [13, 14, 15, 16]
copy
let copy: array<'a> => array<'a>
copy(a)
Returns a copy of a; that is; a fresh array containing the same elements as a.
fill
let fill: (array<'a>, ~offset: int, ~len: int, 'a) => unit
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
RESlet arr = Belt.Array.makeBy(5, (i) => i)
Belt.Array.fill(arr, ~offset=2, ~len=2, 9)
arr == [0, 1, 9, 9, 4]
Belt.Array.fill(arr, ~offset=7, ~len=2, 8)
arr == [0, 1, 9, 9, 4]
blit
let blit:
(
~src: array<'a>,
~srcOffset: int,
~dst: array<'a>,
~dstOffset: int,
~len: int
) =>
unit
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.
RESlet v1 = [10, 11, 12, 13, 14, 15, 16, 17]
let v2 = [20, 21, 22, 23, 24, 25, 26, 27]
Belt.Array.blit(~src=v1, ~srcOffset=4, ~dst=v2, ~dstOffset=2, ~len=3)
v2 == [20, 21, 14, 15, 16, 25, 26, 27]
Belt.Array.blit(~src=v1, ~srcOffset=4, ~dst=v1, ~dstOffset=2, ~len=3)
v1 == [10, 11, 14, 15, 16, 15, 16, 17]
blitUnsafe
let blitUnsafe: (~src: array<'a>, ~srcOffset: int, ~dst: array<'a>, ~dstOffset: int, ~len: int) => unit
Unsafe blit without bounds checking.
forEachU
let forEachU: (array<'a>, (. 'a) => unit) => unit
forEach
let forEach: (array<'a>, 'a => unit) => unit
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.
RESBelt.Array.forEach(["a", "b", "c"], x => Js.log("Item: " ++ x))
/*
prints:
Item: a
Item: b
Item: c
*/
let total = ref(0)
Belt.Array.forEach([1, 2, 3, 4], x => total := total.contents + x)
total.contents == 1 + 2 + 3 + 4
mapU
let mapU: (array<'a>, (. 'a) => 'b) => array<'b>
map
let map: (array<'a>, 'a => 'b) => array<'b>
map(xs, f)
Returns a new array by calling f for each element of xs from the beginning to end.
RESBelt.Array.map([1, 2], (x) => x + 1) == [3, 4]
getByU
let getByU: (array<'a>, (. 'a) => bool) => option<'a>
getBy
let getBy: (array<'a>, 'a => bool) => option<'a>
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.
RESBelt.Array.getBy([1, 4, 3, 2], (x) => mod(x, 2) == 0) == Some(4)
Belt.Array.getBy([15, 13, 11], (x) => mod(x, 2) == 0) == None
getIndexByU
let getIndexByU: (array<'a>, (. 'a) => bool) => option<int>
getIndexBy
let getIndexBy: (array<'a>, 'a => bool) => option<int>
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.
RESBelt.Array.getIndexBy([1, 4, 3, 2], (x) => mod(x, 2) == 0) == Some(1)
Belt.Array.getIndexBy([15, 13, 11], (x) => mod(x, 2) == 0) == None
keepU
let keepU: (array<'a>, (. 'a) => bool) => array<'a>
keep
let keep: (array<'a>, 'a => bool) => array<'a>
keep(xs, p)
Returns a new array that keep all elements satisfy p.
RESBelt.Array.keep([1, 2, 3], (x) => mod(x, 2) == 0) == [2]
keepWithIndexU
let keepWithIndexU: (array<'a>, (. 'a, int) => bool) => array<'a>
keepWithIndex
let keepWithIndex: (array<'a>, ('a, int) => bool) => array<'a>
keepWithIndex(xs, p)
Returns a new array that keep all elements satisfy p.
RESBelt.Array.keepWithIndex([1, 2, 3], (_x, i) => i == 1) == [2]
keepMapU
let keepMapU: (array<'a>, (. 'a) => option<'b>) => array<'b>
keepMap
let keepMap: (array<'a>, 'a => option<'b>) => array<'b>
keepMap(xs, p)
Returns a new array that keep all elements that return a non-None applied p.
RESBelt.Array.keepMap([1, 2, 3], x =>
if mod(x, 2) == 0 {
Some(x)
} else {
None
}
)
== [2]
forEachWithIndexU
let forEachWithIndexU: (array<'a>, (. int, 'a) => unit) => unit
forEachWithIndex
let forEachWithIndex: (array<'a>, (int, 'a) => unit) => unit
forEachWithIndex(xs, f)
The same as Belt_Array.forEach;
except that f is supplied two arguments: the index starting from 0 and the element from xs.
RESBelt.Array.forEachWithIndex(["a", "b", "c"], (i, x) => Js.log("Item " ++ Belt.Int.toString(i) ++ " is " ++ x))
/*
prints:
Item 0 is a
Item 1 is b
Item 2 is cc
*/
let total = ref(0)
Belt.Array.forEachWithIndex([10, 11, 12, 13], (i, x) => total := total.contents + x + i)
total.contents == 0 + 10 + 1 + 11 + 2 + 12 + 3 + 13
mapWithIndexU
let mapWithIndexU: (array<'a>, (. int, 'a) => 'b) => array<'b>
mapWithIndex
let mapWithIndex: (array<'a>, (int, 'a) => 'b) => array<'b>
mapWithIndex(xs, f)
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.
RESBelt.Array.mapWithIndex([1, 2, 3], (i, x) => i + x) == [0 + 1, 1 + 2, 2 + 3]
partitionU
let partitionU: (array<'a>, (. 'a) => bool) => (array<'a>, array<'a>)
partition
let partition: (array<'a>, 'a => bool) => (array<'a>, array<'a>)
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
RESBelt.Array.partition([1, 2, 3, 4, 5], (x) => mod(x, 2) == 0) == ([2, 4], [1, 3, 5])
Belt.Array.partition([1, 2, 3, 4, 5], (x) => mod(x, 2) != 0) == ([1, 3, 5], [2, 4])
reduceU
let reduceU: (array<'b>, 'a, (. 'a, 'b) => 'a) => 'a
reduce
let reduce: (array<'b>, 'a, ('a, 'b) => 'a) => 'a
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.
RESBelt.Array.reduce([2, 3, 4], 1, (a, b) => a + b) == 10
Belt.Array.reduce(["a", "b", "c", "d"], "", (a, b) => a ++ b) == "abcd"
reduceReverseU
let reduceReverseU: (array<'b>, 'a, (. 'a, 'b) => 'a) => 'a
reduceReverse
let reduceReverse: (array<'b>, 'a, ('a, 'b) => 'a) => 'a
reduceReverse(xs, init, f)
Works like Belt_Array.reduce; except that function f is applied to each item of xs from the last back to the first.
RESBelt.Array.reduceReverse(["a", "b", "c", "d"], "", (a, b) => a ++ b) == "dcba"
reduceReverse2U
let reduceReverse2U: (array<'a>, array<'b>, 'c, (. 'c, 'a, 'b) => 'c) => 'c
reduceReverse2
let reduceReverse2: (array<'a>, array<'b>, 'c, ('c, 'a, 'b) => 'c) => 'c
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.
RESBelt.Array.reduceReverse2([1, 2, 3], [1, 2], 0, (acc, x, y) => acc + x + y) == 6
reduceWithIndexU
let reduceWithIndexU: (array<'a>, 'b, (. 'b, 'a, int) => 'b) => 'b
reduceWithIndex
let reduceWithIndex: (array<'a>, 'b, ('b, 'a, int) => 'b) => 'b
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.
RESBelt.Array.reduceWithIndex([1, 2, 3, 4], 0, (acc, x, i) => acc + x + i) == 16
someU
let someU: (array<'a>, (. 'a) => bool) => bool
some
let some: (array<'a>, 'a => bool) => bool
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.
RESBelt.Array.some([2, 3, 4], (x) => mod(x, 2) == 1) == true
Belt.Array.some([(-1), (-3), (-5)], (x) => x > 0) == false
everyU
let everyU: (array<'a>, (. 'a) => bool) => bool
every
let every: (array<'a>, 'a => bool) => bool
every(xs, p)
Returns true if all elements satisfy p; where p is a predicate: a function taking an element and returning a bool.
RESBelt.Array.every([1, 3, 5], (x) => mod(x, 2) == 1) == true
Belt.Array.every([1, (-3), 5], (x) => x > 0) == false
every2U
let every2U: (array<'a>, array<'b>, (. 'a, 'b) => bool) => bool
every2
let every2: (array<'a>, array<'b>, ('a, 'b) => bool) => bool
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)))
RESBelt.Array.every2([1, 2, 3], [0, 1], (a, b) => a > b) == true
Belt.Array.every2([], [1], (x, y) => x > y) == true
Belt.Array.every2([2, 3], [1], (x, y) => x > y) == true
Belt.Array.every2([0, 1], [5, 0], (x, y) => x > y) == false
some2U
let some2U: (array<'a>, array<'b>, (. 'a, 'b) => bool) => bool
some2
let some2: (array<'a>, array<'b>, ('a, 'b) => bool) => bool
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)))
RESBelt.Array.some2([0, 2], [1, 0, 3], (a, b) => a > b) == true
Belt.Array.some2([], [1], (x, y) => x > y) == false
Belt.Array.some2([2, 3], [1, 4], (x, y) => x > y) == true
cmpU
let cmpU: (array<'a>, array<'a>, (. 'a, 'a) => int) => int
cmp
let cmp: (array<'a>, array<'a>, ('a, 'a) => int) => int
cmp(xs, ys, f)
Compared by length if length(xs) != length(ys); returning -1 if length(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.
RESBelt.Array.cmp([1, 3, 5], [1, 4, 2], (a, b) => compare(a, b)) == -1
Belt.Array.cmp([1, 3, 5], [1, 2, 3], (a, b) => compare(a, b)) == 1
Belt.Array.cmp([1, 3, 5], [1, 3, 5], (a, b) => compare(a, b)) == 0
eqU
let eqU: (array<'a>, array<'a>, (. 'a, 'a) => bool) => bool
eq
let eq: (array<'a>, array<'a>, ('a, 'a) => bool) => bool
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 truefalse otherwise
RESBelt.Array.eq([1, 2, 3], [(-1), (-2), (-3)], (a, b) => abs(a) == abs(b)) == true
truncateToLengthUnsafe
let truncateToLengthUnsafe: (array<'a>, int) => unit
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.
RESlet arr = ["ant", "bee", "cat", "dog", "elk"]
Belt.Array.truncateToLengthUnsafe(arr, 3)
arr == ["ant", "bee", "cat"]
