array

☰std/array/any

Checks if the given array is present and it is not empty (contains at least one element).

Type signature

<T>(xs?: T[]) => boolean

Examples

any([]);
// ⇒ false
Try in REPL 
any([1, 2, 3]);
// ⇒ true
Try in REPL

Questions

  • How to check if an array is empty?
  • How to check if an array is empty or null or undefined?
  • How to check if an array is empty or not?
  • How to check if an array is empty or doesn't exist?

TypeScript source • JavaScript source

☰std/array/are

Checks if the given arguments are all `Arrays`.

Type signature

<T>(...xs: T[]) => boolean

Examples

are([2, 3]);
// ⇒ true
Try in REPL 
are([1, 2, 3], []);
// ⇒ true
Try in REPL 
are([1, 2, 3], 8, [1, 3], "test");
// ⇒ false
Try in REPL

Questions

  • How to check if all the given values are arrays?

TypeScript source • JavaScript source

☰std/array/chunk

Splits the given array into an array of chunks of up to the given length.

Type signature

(count: number) => <T>(xs: T[]) => T[] | T[][]

Examples

chunk(2)(["a", "b", "c", "d"]);
// ⇒ [['a', 'b'], ['c', 'd']]
Try in REPL 
chunk(3)(["a", "b", "c", "d"]);
// ⇒ [['a', 'b', 'c'], ['d']]
Try in REPL

Questions

  • How to split an array into chunks?
  • How to split an array into chunks of the same size?

TypeScript source • JavaScript source

☰std/array/difference

Computes a set difference between the two given arrays.

Type signature

<T>(xs: T[], ys: T[]) => T[]

Examples

difference(
  [1, 2, 3, 4, 5, 6],
  [2, 4],
);
// ⇒ [1, 3, 5, 6]
Try in REPL

Questions

  • How to find elements which are present in the first array and not in the second?

TypeScript source • JavaScript source

☰std/array/differs

Checks if two arrays are not equal.

Type signature

<T>(xs?: T[], ys?: T[]) => boolean

Examples

differs([1, 2, 3], [1, 2]);
// ⇒ true
Try in REPL 
differs([1, 2, 3], [1, 2, 3]);
// ⇒ false
Try in REPL

Questions

  • How to check if two arrays differ?
  • How to check if two arrays are not equal?
  • How to check if two arrays are equal or not?

TypeScript source • JavaScript source

☰std/array/duplicates

Lists all the duplicated values in the given array.

Type signature

<T>(xs: T[]) => T[]

Examples

duplicates([
  1, 2, 3, 4, 3, 4, 3, 6,
]);
// ⇒ [3, 4, 3]
Try in REPL

Questions

  • How to find duplicates in an array?

TypeScript source • JavaScript source

☰std/array/empty

Empty array.

Type signature

unknown[]

Examples

empty;
// ⇒ []
Try in REPL

Questions

  • How to get an empty array?

TypeScript source • JavaScript source

☰std/array/exact

Takes exactly the given count of elements.

Type signature

(count: number) => <T>(xs: T[]) => T[]

Examples

exact(5)([1, 2, 3]);
// ⇒ [1, 2, 3, undefined, undefined]
Try in REPL 
exact(2)([1, 2, 3]);
// ⇒ [1, 2]
Try in REPL

Questions

  • How to get exactly N elements out of an array?

TypeScript source • JavaScript source

☰std/array/except

Filters out the given value.

Type signature

<T>(y: T) => (xs: T[]) => T[]

Examples

except(2)([1, 2, 3, 4, 5]);
// ⇒ [1, 3, 4, 5]
Try in REPL 
except(2)([1, 2, 2, 4, 2]);
// ⇒ [1, 4]
Try in REPL

Questions

  • How to get all the values of an array except the given one?

TypeScript source • JavaScript source

☰std/array/filterInPlace

Filters the given array with the given predicate just like Array.filter but does it in-place thus mutates the original array.

Type signature

<T>(f: (value: T, index: number, context: T[]) => boolean) => (xs: T[]) => T[]

Examples

const xs = [1, 2, 3, 4, 5, 6, 7];
const odd = (x) => x % 2 === 1;

const ys = filterInPlace(odd)(xs);

ys === xs;
// ⇒ true
ys;
// ⇒ [1, 3, 5, 7]
Try in REPL

Questions

  • How to filter an array in place?

TypeScript source • JavaScript source

☰std/array/find

Finds an element by a predicate function within the given array, otherwise, it returns the given fallback value or undefined when fallback is not present.

Type signature

<T>(predicate: (value: T, index: number, context: T[]) => boolean, fallback?: T) => (xs: T[]) => T

Examples

find((x) => x > 2)([1, 2, 3, 5, 7]);
// ⇒ 3
Try in REPL 
find((x) => x > 2)([
  1, 2, -3, -5, -7,
]);
// ⇒ undefined
Try in REPL

Questions

  • How to find an element of an array by a given predicate?

TypeScript source • JavaScript source

☰std/array/first

Returns the first element or undefined when there are no elements in the given array.

Type signature

<T>([x]: T[]) => T | undefined

Examples

first([1, 2, 3]);
// ⇒ 1
Try in REPL 
first([]);
// ⇒ undefined
Try in REPL

Questions

  • How to get the first element of an array?

TypeScript source • JavaScript source

☰std/array/flatMap

Maps and flattens the result.

Type signature

<T, TResult>(f: (value: T, index: number, context: T[]) => TResult[]) => (xs: T[]) => TResult[]

Examples

flatMap((text) => [...text])([
  "test",
  "123",
]);
// ⇒ ["t", "e", "s", "t", "1", "2", "3"]
Try in REPL

Questions

  • How to flat map an array?
  • How to map and then flatten an array?

TypeScript source • JavaScript source

☰std/array/flatten

Flattens the nested arrays by a single level.

Type signature

<T>(xs: T[]) => T[]

Examples

flatten([1, [2, 3], 4, [5, 6]]);
// ⇒ [1, 2, 3, 4, 5, 6]
Try in REPL 
flatten([
  1,
  [2, [3, 6]],
  4,
  [5, 6],
]);
// ⇒ [1, 2, [3, 6], 4, 5, 6]
Try in REPL

Questions

  • How to flatten an array?

TypeScript source • JavaScript source

☰std/array/insert

Inserts the given item to the array at a specific index.

Type signature

(index: number) => <T>(item: T) => ([...xs]: T[]) => T[]

Examples

insert(0)("d")(["a", "b", "c"]);
// ⇒ ['d', 'a', 'b', 'c']
Try in REPL 
insert(1)("d")(["a", "b", "c"]);
// ⇒ ['a', 'd', 'b', 'c']
Try in REPL

Questions

  • How to insert an element to an array at a given position?

TypeScript source • JavaScript source

☰std/array/intersection

Finds common elements between both arrays.

Type signature

<T>(xs: T[], ys: T[]) => T[]

Examples

intersection(
  [1, 2, 3, 4, 5],
  [5, 5, 3, 2],
);
// ⇒ [2, 3, 5]
Try in REPL

Questions

  • How to find common elements present in both arrays?

TypeScript source • JavaScript source

☰std/array/is

Checks if the given argument is an array.

Type signature

(value?: unknown) => boolean

Examples

is([1, 2, 3]);
// ⇒ true
Try in REPL 
is({ a: 5 });
// ⇒ false
Try in REPL

Questions

  • How to check if a value is an array?

TypeScript source • JavaScript source

☰std/array/last

Returns the last element or undefined when there are no elements in the given array.

Type signature

<T>(xs: T[]) => T | undefined

Examples

last([1, 2, 3]);
// ⇒ 3
Try in REPL 
last([]);
// ⇒ undefined
Try in REPL

Questions

  • How to get the last element of an array?

TypeScript source • JavaScript source

☰std/array/length

Returns the number of elements in the given array.

Type signature

<T>(xs: T[]) => number

Examples

length([true, 1]);
// ⇒ 2
Try in REPL 
length([1, 2, 3]);
// ⇒ 3
Try in REPL 
length([]);
// ⇒ 0
Try in REPL

Questions

  • How to check an array's length?
  • How to compute an array's length?
  • How to check the size of an array?
  • How to check the number of elements in an array?

TypeScript source • JavaScript source

☰std/array/lengthDiffers

Checks if lengths of the given arrays differ.

Type signature

<T1, T2>(a: T1[], b: T2[]) => boolean

Examples

lengthDiffers([1, 2, 3], [1, 2]);
// ⇒ true
Try in REPL 
lengthDiffers([6, 7], [1, 2]);
// ⇒ false
Try in REPL

Questions

  • How to check if array lengths differ?
  • How to check if the given arrays have different lengths?

TypeScript source • JavaScript source

☰std/array/map

Maps the given array with the given functions.

Type signature

<T>(...fs: ((x: T) => T)[]) => (xs: T[]) => T[]

Examples

map((x) => x * x)([1, 2, 3]);
// ⇒ [1, 4, 9]
Try in REPL 
map(
  (x) => x * x,
  (x) => x + 1,
)([1, 2, 3]);
// ⇒ [2, 5, 10]
Try in REPL

Questions

  • How to map an array?

TypeScript source • JavaScript source

☰std/array/midpoint

Returns the middle element or the right one when the number of elements is even.

Type signature

<T>(xs: T[]) => T | undefined

Examples

midpoint([1, 2, 3, 4, 5]);
// ⇒ 3
Try in REPL 
midpoint([1, 2, 3, 4]);
// ⇒ 3
Try in REPL

Questions

  • How to get the element in the middle of an array?
  • How to get the middle element of an array?

TypeScript source • JavaScript source

☰std/array/minMax

Computes minimum and maximum values of the given array in a single run.

Type signature

(xs: number[]) => number[]

Examples

minMax([
  10, 5, 3, -5, -4, 23, 32, 8, 1, 0,
]);
// ⇒ [-5, 32]
Try in REPL 
minMax([1]);
// ⇒ [1, 1]
Try in REPL 
minMax([]);
// ⇒ [undefined, undefined]
Try in REPL

Questions

  • How to find the minimum and maximum values of an array?
  • How to get the min/max element of an array?

TypeScript source • JavaScript source

☰std/array/multiple

Checks if the given array contains more than one element.

Type signature

<T>(xs: T[]) => boolean

Examples

multiple([1, 2, 3]);
// ⇒ true
Try in REPL 
multiple([1, 2]);
// ⇒ true
Try in REPL 
multiple([1]);
// ⇒ false
Try in REPL 
multiple([]);
// ⇒ false
Try in REPL

Questions

  • How to check if an array contains multiple elements?
  • How to check whether multiple values exist within an array?

TypeScript source • JavaScript source

☰std/array/none

Checks if the given array is empty.

Type signature

<T>(xs?: T[]) => boolean

Examples

none([]);
// ⇒ true
Try in REPL 
none([1, 2, 3]);
// ⇒ false
Try in REPL

Questions

  • How to check if an array is empty?

TypeScript source • JavaScript source

☰std/array/partition

Partitions the given array to the ones that pass the given predicate function and the ones that do not. By [convention of the Haskell's Data.Either](http://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Either.html), values that pass the predicate are placed at the right.

Type signature

<T>(predicate: (x: T) => boolean) => (xs: T[]) => readonly [T[], T[]]

Examples

partition((x) => x % 2 === 1)([
  1, 2, 3, 4, 5,
]);
// ⇒ [[2, 4], [1, 3, 5]])
Try in REPL

Questions

  • How to partition an array based on a condition?
  • How to divide an array by a filter function?

TypeScript source • JavaScript source

☰std/array/pop

Returns the given array without the last element.

Type signature

<T>(xs: T[]) => T[]

Examples

pop([1, 2, 3, 4]); // ⇒ [1, 2, 3]
Try in REPL 
pop([]); // ⇒ []
Try in REPL

Questions

  • How to get an array without the last element?
  • How to remove the last element from an array?

TypeScript source • JavaScript source

☰std/array/range

Generates an array of numbers from 0 to n - 1.

Type signature

(n: number) => number[]

Examples

range(3);
// ⇒ [0, 1, 2]
Try in REPL

Questions

  • How to create an array of all integers from 0 to N exclusive?

TypeScript source • JavaScript source

☰std/array/removeAt

Removes an element at the given index from the given array.

Type signature

(index: number) => <T>(xs: T[]) => T[]

Examples

removeAt(3)([1, 2, 3, 4, 5, 6]);
// ⇒ [1, 2, 3, 5, 6]
Try in REPL

Questions

  • How to remove an item from an array at a particular index?

TypeScript source • JavaScript source

☰std/array/repeat

Repeats the given element by the given count of times.

Type signature

(count: number) => <T>(value: T) => T[]

Examples

repeat(3)("test");
// ⇒ ["test", "test", "test"]
Try in REPL

Questions

  • How to repeat a value N times?

TypeScript source • JavaScript source

☰std/array/reverse

Reverses the given array without mutating it (in contrast to Array.reverse).

Type signature

<T>(xs: T[]) => T[]

Examples

reverse([1, 2, 3, 4, 5]);
// ⇒ [5, 4, 3, 2, 1]
Try in REPL

Questions

  • How to reverse an array without mutating it?

TypeScript source • JavaScript source

☰std/array/reverseIf

Reverses the given array when enabled.

Type signature

(enabled: boolean) => <T>(xs: T[]) => T[]

Examples

reverseIf(true)([1, 2, 3, 4, 5]);
// ⇒ [5, 4, 3, 2, 1]
Try in REPL 
reverseIf(false)([1, 2, 3, 4, 5]);
// ⇒ [1, 2, 3, 4, 5]
Try in REPL

Questions

  • How to reverse an array without mutating it only when a condition is satisfied?

TypeScript source • JavaScript source

☰std/array/second

Returns the second element or undefined when there are less than two elements in the given array.

Type signature

<T>(xs: T[]) => T | undefined

Examples

second([1, 2, 3, 4, 5]);
// ⇒ 2
Try in REPL 
second([1]);
// ⇒ undefined
Try in REPL 
second([]);
// ⇒ undefined
Try in REPL

Questions

  • How to get the second element of an array?

TypeScript source • JavaScript source

☰std/array/secondToLast

Returns the second to last element or undefined when there are less than two elements in the given array.

Type signature

<T>(xs: T[]) => T | undefined

Examples

secondToLast([1, 2, 3, 4, 5]);
// ⇒ 4
Try in REPL 
secondToLast([1]);
// ⇒ undefined
Try in REPL 
secondToLast([]);
// ⇒ undefined
Try in REPL

Questions

  • How to get the second to last element of an array?

TypeScript source • JavaScript source

☰std/array/shift

Shifts the given array to the left and circulates the elements back by modulo of the array's length.

Type signature

(count: number) => <T>(xs: T[]) => T[]

Examples

shift(1)([1, 2, 3, 4, 5]);
// ⇒ [2, 3, 4, 5, 1]
Try in REPL 
shift(2)([1, 2, 3, 4, 5]);
// ⇒ [3, 4, 5, 1, 2]
Try in REPL 
shift(3)([1, 2, 3, 4, 5]);
// ⇒ [4, 5, 1, 2, 3]
Try in REPL

Questions

  • How to shift an array?

TypeScript source • JavaScript source

☰std/array/shuffle

Shuffles the given array in random order with Math.random as the default.

Type signature

<T>(xs: T[], random?: () => number) => T[]

Examples

let i = 0;

const random = () =>
  [
    0.013606630487694282,
    0.21052486239086554,
    0.28299838254636556,
    0.696161009199874,
    0.32165320593537117,
  ][i++];

shuffle([1, 2, 3, 4, 5], random); // => [3, 5, 4, 2, 1]
Try in REPL

Questions

  • How to shuffle an array?

TypeScript source • JavaScript source

☰std/array/shuffleInPlace

Shuffles the given array in-place in random order with Math.random as the default.

Type signature

<T>(xs: T[], random?: () => number) => T[]

Examples

let i = 0;

const random = () =>
  [
    0.013606630487694282,
    0.21052486239086554,
    0.28299838254636556,
    0.696161009199874,
    0.32165320593537117,
  ][i++];

shuffleInPlace(
  [1, 2, 3, 4, 5],
  random,
); // => [3, 5, 4, 2, 1]
Try in REPL

Questions

  • How to shuffle an array in place?

TypeScript source • JavaScript source

☰std/array/single

Checks if the given array contains exactly one element.

Type signature

<T>(xs: T[]) => boolean

Examples

single([1]);
// ⇒ true
Try in REPL 
single([1, 2, 3]);
// ⇒ false
Try in REPL 
single([]);
// ⇒ false
Try in REPL

Questions

  • How to check if an array contains only one element?

TypeScript source • JavaScript source

☰std/array/skip

Skips the given count of elements from the given array.

Type signature

(count: number) => <T>(xs: T[]) => T[]

Examples

skip(2)([1, 2, 3, 4, 5]);
// ⇒ [3, 4, 5]
Try in REPL

Questions

  • How to skip the first few elements of an array?

TypeScript source • JavaScript source

☰std/array/slidingWindow

Returns a new array composed of tuples of the given sliding window length of consecutive elements.

Type signature

(count: number) => <T>(xs: T[]) => T[][]

Examples

slidingWindow(2)([1, 2, 3, 4]);
// ⇒ [[1, 2], [2, 3], [3, 4]]
Try in REPL 
slidingWindow(3)([1, 2, 3, 4, 5]);
// ⇒ [[1, 2, 3], [2, 3, 4], [3, 4, 5]]
Try in REPL 
slidingWindow(1)([
  1, 2, 3, 4, 5, 6,
]);
// ⇒ [[1], [2], [3], [4], [5], [6]]
Try in REPL

Questions

  • How to iterate an array pairwise?

TypeScript source • JavaScript source

☰std/array/sort

Sorts the given array without mutating it.

Type signature

<T>(f?: (a: T, b: T) => number) => (xs: T[]) => T[]

Examples

sort((a, b) => a - b)([
  13, 79, 20, 69, 44, 67, 18, 95,
  26, 55,
]);
// ⇒ [13, 18, 20, 26, 44, 55, 67, 69, 79, 95]
Try in REPL

Questions

  • How to sort an array without mutating it?

TypeScript source • JavaScript source

☰std/array/sum

Sums the given array of numbers.

Type signature

(xs: number[]) => number

Examples

sum([1, 2, 3, 4, 5]);
// ⇒ 15
Try in REPL

Questions

  • How to sum elements of an array?

TypeScript source • JavaScript source

☰std/array/take

Takes up to a given count of elements.

Type signature

(count: number) => <T>(xs: T[]) => T[]

Examples

take(2)([1, 2, 3, 4, 5]);
// ⇒ [1, 2]
Try in REPL 
take(10)([1, 2, 3, 4, 5]);
// ⇒ [1, 2, 3, 4, 5]
Try in REPL

Questions

  • How to get the first N number of elements from an array?

TypeScript source • JavaScript source

☰std/array/unique

Returns unique elements of the given array.

Type signature

<T>(xs: T[]) => T[]

Examples

unique([1, 2, 3, 4, 3, 4, 3, 6]);
// ⇒ [1, 2, 3, 4, 6]
Try in REPL

Questions

  • How to find all unique values in an array?

TypeScript source • JavaScript source

☰std/array/uniqueBy

Filters out duplicated values based on the result of the given key selector.

Type signature

<T, TResult>(f: (x: T) => TResult) => (xs: T[]) => T[]

Examples

uniqueBy(({ id }) => id)([
  { id: 1, value: "a" },
  { id: 2, value: "b" },
  { id: 1, value: "c" },
]);
// ⇒ [{ id: 1, value: 'c' }, { id: 2, value: 'b' }]
Try in REPL

Questions

  • How to find all unique values in an array by some predicate?

TypeScript source • JavaScript source

☰std/array/zip

Zips the given arrays together into pairs.

Type signature

(xs: unknown[], ys: unknown[]) => [unknown, unknown][]

Examples

zip([1, 2, 3], [4, 5, 6]);
// ⇒ [[1, 4],[2, 5],[3, 6]]
Try in REPL

Questions

  • How to zip two arrays?

TypeScript source • JavaScript source

☰std/array/zipN

Zips the given arrays together into pairs.

Type signature

<T>(...xs: T[][]) => T[][]

Examples

zipN([1, 2, 3], [4, 5, 6]);
// ⇒ [[1, 4], [2, 5], [3, 6]]
Try in REPL 
zipN(
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
);
// ⇒ [[1, 4, 7], [2, 5, 8], [3, 6, 9]]
Try in REPL 
zipN([1, 2], [4, 5, 6], [7, 8, 9]);
// ⇒ [[1, 4, 7],[2, 5, 8]]
Try in REPL

Questions

  • How to zip multiple arrays?

TypeScript source • JavaScript source

☰std/array/zipWith

Zips the given arrays together with the given function.

Type signature

<T1, T2>(f?: (x: T1, y: T2) => [T1, T2]) => (xs: T1[], ys: T2[]) => [T1, T2][]

Examples

zipWith((x, y) => x * x + y)(
  [1, 2, 3],
  [4, 5, 6],
);
// ⇒ [5, 9, 15]
Try in REPL

Questions

  • How to zip two arrays with a given function?

TypeScript source • JavaScript source