Data.Array
- Package
- arrays
- Repository
- purerl/purescript-arrays
Helper functions for working with immutable Javascript arrays.
Note: Depending on your use-case, you may prefer to use Data.List
or
Data.Sequence
instead, which might give better performance for certain
use cases. This module is useful when integrating with JavaScript libraries
which use arrays, but immutable arrays are not a practical data structure
for many use cases due to their poor asymptotics.
In addition to the functions in this module, Arrays have a number of useful instances:
Functor
, which providesmap :: forall a b. (a -> b) -> Array a -> Array b
Apply
, which provides(<*>) :: forall a b. Array (a -> b) -> Array a -> Array b
. This function works a bit like a Cartesian product; the result array is constructed by applying each function in the first array to each value in the second, so that the result array ends up with a length equal to the product of the two arguments' lengths.Bind
, which provides(>>=) :: forall a b. (a -> Array b) -> Array a -> Array b
(this is the same asconcatMap
).Semigroup
, which provides(<>) :: forall a. Array a -> Array a -> Array a
, for concatenating arrays.Foldable
, which provides a slew of functions for folding (also known as reducing) arrays down to one value. For example,Data.Foldable.or
tests whether an array ofBoolean
values contains at least onetrue
value.Traversable
, which provides the PureScript version of a for-loop, allowing you to STAI.iterate over an array and accumulate effects.
#fromFoldable Source
fromFoldable :: forall f. Foldable f => f ~> Array
Convert a Foldable
structure into an Array
.
fromFoldable (Just 1) = [1]
fromFoldable (Nothing) = []
#toUnfoldable Source
toUnfoldable :: forall f. Unfoldable f => Array ~> f
Convert an Array
into an Unfoldable
structure.
#(..) Source
Operator alias for Data.Array.range (non-associative / precedence 8)
An infix synonym for range
.
2 .. 5 = [2, 3, 4, 5]
#some Source
some :: forall f a. Alternative f => Lazy (f (Array a)) => f a -> f (Array a)
Attempt a computation multiple times, requiring at least one success.
The Lazy
constraint is used to generate the result lazily, to ensure
termination.
#many Source
many :: forall f a. Alternative f => Lazy (f (Array a)) => f a -> f (Array a)
Attempt a computation multiple times, returning as many successful results as possible (possibly zero).
The Lazy
constraint is used to generate the result lazily, to ensure
termination.
#(:) Source
Operator alias for Data.Array.cons (right-associative / precedence 6)
An infix alias for cons
.
1 : [2, 3, 4] = [1, 2, 3, 4]
Note, the running time of this function is O(n)
.
#uncons Source
uncons :: forall a. Array a -> Maybe { head :: a, tail :: Array a }
Break an array into its first element and remaining elements.
Using uncons
provides a way of writing code that would use cons patterns
in Haskell or pre-PureScript 0.7:
f (x : xs) = something
f [] = somethingElse
Becomes:
f arr = case uncons arr of
Just { head: x, tail: xs } -> something
Nothing -> somethingElse
#(!!) Source
Operator alias for Data.Array.index (left-associative / precedence 8)
An infix version of index
.
sentence = ["Hello", "World", "!"]
sentence !! 0 = Just "Hello"
sentence !! 7 = Nothing
#elemLastIndex Source
elemLastIndex :: forall a. Eq a => a -> Array a -> Maybe Int
Find the index of the last element equal to the specified element.
elemLastIndex "a" ["a", "b", "a", "c"] = Just 2
elemLastIndex "Earth" ["Hello", "World", "!"] = Nothing
#findLastIndex Source
findLastIndex :: forall a. (a -> Boolean) -> Array a -> Maybe Int
Find the last index for which a predicate holds.
findLastIndex (contains $ Pattern "b") ["a", "bb", "b", "d"] = Just 2
findLastIndex (contains $ Pattern "x") ["a", "bb", "b", "d"] = Nothing
#updateAtIndices Source
updateAtIndices :: forall t a. Foldable t => t (Tuple Int a) -> Array a -> Array a
Change the elements at the specified indices in index/value pairs. Out-of-bounds indices will have no effect.
updates = [Tuple 0 "Hi", Tuple 2 "." , Tuple 10 "foobar"]
updateAtIndices updates ["Hello", "World", "!"] = ["Hi", "World", "."]
#modifyAt Source
modifyAt :: forall a. Int -> (a -> a) -> Array a -> Maybe (Array a)
Apply a function to the element at the specified index, creating a new
array, or returning Nothing
if the index is out of bounds.
modifyAt 1 toUpper ["Hello", "World"] = Just ["Hello", "WORLD"]
modifyAt 10 toUpper ["Hello", "World"] = Nothing
#modifyAtIndices Source
modifyAtIndices :: forall t a. Foldable t => t Int -> (a -> a) -> Array a -> Array a
Apply a function to the element at the specified indices, creating a new array. Out-of-bounds indices will have no effect.
indices = [1, 3]
modifyAtIndices indices toUpper ["Hello", "World", "and", "others"]
= ["Hello", "WORLD", "and", "OTHERS"]
#alterAt Source
alterAt :: forall a. Int -> (a -> Maybe a) -> Array a -> Maybe (Array a)
Update or delete the element at the specified index by applying a
function to the current value, returning a new array or Nothing
if the
index is out-of-bounds.
alterAt 1 (stripSuffix $ Pattern "!") ["Hello", "World!"]
= Just ["Hello", "World"]
alterAt 1 (stripSuffix $ Pattern "!!!!!") ["Hello", "World!"]
= Just ["Hello"]
alterAt 10 (stripSuffix $ Pattern "!") ["Hello", "World!"] = Nothing
#intersperse Source
intersperse :: forall a. a -> Array a -> Array a
Inserts the given element in between each element in the array. The array must have two or more elements for this operation to take effect.
intersperse " " [ "a", "b" ] == [ "a", " ", "b" ]
intersperse 0 [ 1, 2, 3, 4, 5 ] == [ 1, 0, 2, 0, 3, 0, 4, 0, 5 ]
If the array has less than two elements, the input array is returned.
intersperse " " [] == []
intersperse " " ["a"] == ["a"]
#partition Source
partition :: forall a. (a -> Boolean) -> Array a -> { no :: Array a, yes :: Array a }
Partition an array using a predicate function, creating a set of new arrays. One for the values satisfying the predicate function and one for values that don't.
partition (_ > 0) [-1, 4, -5, 7] = { yes: [4, 7], no: [-1, -5] }
#splitAt Source
splitAt :: forall a. Int -> Array a -> { after :: Array a, before :: Array a }
Splits an array into two subarrays, where before
contains the elements
up to (but not including) the given index, and after
contains the rest
of the elements, from that index on.
>>> splitAt 3 [1, 2, 3, 4, 5]
{ before: [1, 2, 3], after: [4, 5] }
Thus, the length of (splitAt i arr).before
will equal either i
or
length arr
, if that is shorter. (Or if i
is negative the length will
be 0.)
splitAt 2 ([] :: Array Int) == { before: [], after: [] }
splitAt 3 [1, 2, 3, 4, 5] == { before: [1, 2, 3], after: [4, 5] }
#filterA Source
filterA :: forall a f. Applicative f => (a -> f Boolean) -> Array a -> f (Array a)
Filter where the predicate returns a Boolean
in some Applicative
.
powerSet :: forall a. Array a -> Array (Array a)
powerSet = filterA (const [true, false])
#mapMaybe Source
mapMaybe :: forall a b. (a -> Maybe b) -> Array a -> Array b
Apply a function to each element in an array, keeping only the results which contain a value, creating a new array.
parseEmail :: String -> Maybe Email
parseEmail = ...
mapMaybe parseEmail ["a.com", "hello@example.com", "--"]
= [Email {user: "hello", domain: "example.com"}]
#mapWithIndex Source
mapWithIndex :: forall a b. (Int -> a -> b) -> Array a -> Array b
Apply a function to each element in an array, supplying a generated zero-based index integer along with the element, creating an array with the new elements.
prefixIndex index element = show index <> element
mapWithIndex prefixIndex ["Hello", "World"] = ["0Hello", "1World"]
#intercalate Source
intercalate :: forall a. Monoid a => a -> Array a -> a
#scanl Source
scanl :: forall a b. (b -> a -> b) -> b -> Array a -> Array b
Fold a data structure from the left, keeping all intermediate results
instead of only the final result. Note that the initial value does not
appear in the result (unlike Haskell's Prelude.scanl
).
scanl (+) 0 [1,2,3] = [1,3,6]
scanl (-) 10 [1,2,3] = [9,7,4]
#scanr Source
scanr :: forall a b. (a -> b -> b) -> b -> Array a -> Array b
Fold a data structure from the right, keeping all intermediate results
instead of only the final result. Note that the initial value does not
appear in the result (unlike Haskell's Prelude.scanr
).
scanr (+) 0 [1,2,3] = [6,5,3]
scanr (flip (-)) 10 [1,2,3] = [4,5,7]
#sortBy Source
sortBy :: forall a. (a -> a -> Ordering) -> Array a -> Array a
Sort the elements of an array in increasing order, where elements are compared using the specified partial ordering, creating a new array. Sorting is stable: the order of elements is preserved if they are equal according to the specified partial ordering.
compareLength a b = compare (length a) (length b)
sortBy compareLength [[1, 2, 3], [7, 9], [-2]] = [[-2],[7,9],[1,2,3]]
#sortWith Source
sortWith :: forall a b. Ord b => (a -> b) -> Array a -> Array a
Sort the elements of an array in increasing order, where elements are sorted based on a projection. Sorting is stable: the order of elements is preserved if they are equal according to the projection.
sortWith (_.age) [{name: "Alice", age: 42}, {name: "Bob", age: 21}]
= [{name: "Bob", age: 21}, {name: "Alice", age: 42}]
#span Source
span :: forall a. (a -> Boolean) -> Array a -> { init :: Array a, rest :: Array a }
Split an array into two parts:
- the longest initial subarray for which all elements satisfy the specified predicate
- the remaining elements
span (\n -> n % 2 == 1) [1,3,2,4,5] == { init: [1,3], rest: [2,4,5] }
Running time: O(n)
.
#group Source
group :: forall a. Eq a => Array a -> Array (NonEmptyArray a)
Group equal, consecutive elements of an array into arrays.
group [1, 1, 2, 2, 1] == [NonEmptyArray [1, 1], NonEmptyArray [2, 2], NonEmptyArray [1]]
#groupAll Source
groupAll :: forall a. Ord a => Array a -> Array (NonEmptyArray a)
Group equal elements of an array into arrays.
groupAll [1, 1, 2, 2, 1] == [NonEmptyArray [1, 1, 1], NonEmptyArray [2, 2]]
#groupBy Source
groupBy :: forall a. (a -> a -> Boolean) -> Array a -> Array (NonEmptyArray a)
Group equal, consecutive elements of an array into arrays, using the specified equivalence relation to determine equality.
groupBy (\a b -> odd a && odd b) [1, 3, 2, 4, 3, 3]
= [NonEmptyArray [1, 3], NonEmptyArray [2], NonEmptyArray [4], NonEmptyArray [3, 3]]
#groupAllBy Source
groupAllBy :: forall a. (a -> a -> Ordering) -> Array a -> Array (NonEmptyArray a)
Group equal elements of an array into arrays, using the specified comparison function to determine equality.
groupAllBy (comparing Down) [1, 3, 2, 4, 3, 3]
= [NonEmptyArray [4], NonEmptyArray [3, 3, 3], NonEmptyArray [2], NonEmptyArray [1]]
#nubByEq Source
nubByEq :: forall a. (a -> a -> Boolean) -> Array a -> Array a
Remove the duplicates from an array, where element equality is determined by the specified equivalence relation, creating a new array.
This less efficient version of nubBy
only requires an equivalence
relation.
mod3eq a b = a `mod` 3 == b `mod` 3
nubByEq mod3eq [1, 3, 4, 5, 6] = [1, 3, 5]
#unionBy Source
unionBy :: forall a. (a -> a -> Boolean) -> Array a -> Array a -> Array a
Calculate the union of two arrays, using the specified function to determine equality of elements. Note that duplicates in the first array are preserved while duplicates in the second array are removed.
mod3eq a b = a `mod` 3 == b `mod` 3
unionBy mod3eq [1, 5, 1, 2] [3, 4, 3, 3] = [1, 5, 1, 2, 3]
#deleteBy Source
deleteBy :: forall a. (a -> a -> Boolean) -> a -> Array a -> Array a
Delete the first element of an array which matches the specified value, under the equivalence relation provided in the first argument, creating a new array.
mod3eq a b = a `mod` 3 == b `mod` 3
deleteBy mod3eq 6 [1, 3, 4, 3] = [1, 4, 3]
#difference Source
difference :: forall a. Eq a => Array a -> Array a -> Array a
Delete the first occurrence of each element in the second array from the first array, creating a new array.
difference [2, 1] [2, 3] = [1]
Running time: O(n*m)
, where n is the length of the first array, and m is
the length of the second.
#intersectBy Source
intersectBy :: forall a. (a -> a -> Boolean) -> Array a -> Array a -> Array a
Calculate the intersection of two arrays, using the specified equivalence relation to compare elements, creating a new array. Note that duplicates in the first array are preserved while duplicates in the second array are removed.
mod3eq a b = a `mod` 3 == b `mod` 3
intersectBy mod3eq [1, 2, 3] [4, 6, 7] = [1, 3]
#zipWith Source
zipWith :: forall a b c. (a -> b -> c) -> Array a -> Array b -> Array c
Apply a function to pairs of elements at the same index in two arrays, collecting the results in a new array.
If one array is longer, elements will be discarded from the longer array.
For example
zipWith (*) [1, 2, 3] [4, 5, 6, 7] == [4, 10, 18]
#zipWithA Source
zipWithA :: forall m a b c. Applicative m => (a -> b -> m c) -> Array a -> Array b -> m (Array c)
A generalization of zipWith
which accumulates results in some
Applicative
functor.
sndChars = zipWithA (\a b -> charAt 2 (a <> b))
sndChars ["a", "b"] ["A", "B"] = Nothing -- since "aA" has no 3rd char
sndChars ["aa", "b"] ["AA", "BBB"] = Just ['A', 'B']
#any Source
any :: forall a. (a -> Boolean) -> Array a -> Boolean
Returns true if at least one array element satisfies the given predicate, iterating the array only as necessary and stopping as soon as the predicate yields true.
any (_ > 0) [] = False
any (_ > 0) [-1, 0, 1] = True
any (_ > 0) [-1, -2, -3] = False
#unsafeIndex Source
unsafeIndex :: forall a. Partial => Array a -> Int -> a
Find the element of an array at the specified index.
unsafePartial $ unsafeIndex ["a", "b", "c"] 1 = "b"
Using unsafeIndex
with an out-of-range index will not immediately raise a runtime error.
Instead, the result will be undefined. Most attempts to subsequently use the result will
cause a runtime error, of course, but this is not guaranteed, and is dependent on the backend;
some programs will continue to run as if nothing is wrong. For example, in the JavaScript backend,
the expression unsafePartial (unsafeIndex [true] 1)
has type Boolean
;
since this expression evaluates to undefined
, attempting to use it in an if
statement will cause
the else branch to be taken.