Rambda

apply

apply<T = any>(fn: (...args: any[]) => T, args: any[]): T

It applies function fn to the list of arguments.

This is useful for creating a fixed-arity function from a variadic function. fn should be a bound function if context is significant.

const result = R.apply(Math.max, [42, -Infinity, 1337])
// => 1337

Try this R.apply example in Rambda REPL

applySpec

applySpec<Spec extends Record<string, AnyFunction>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> }

:boom: The currying in this function works best with functions with 4 arguments or less. (arity of 4)

const fn = R.applySpec({
  sum: R.add,
  nested: { mul: R.multiply }
})
const result = fn(2, 4) 
// => { sum: 6, nested: { mul: 8 } }

Try this R.applySpec example in Rambda REPL

applyTo

Try this R.applyTo example in Rambda REPL

ascend

Try this R.ascend example in Rambda REPL

assoc

It makes a shallow clone of obj with setting or overriding the property prop with newValue.

:boom: This copies and flattens prototype properties onto the new object as well. All non-primitive properties are copied by reference.

Try this R.assoc example in Rambda REPL

assocPath

assocPath<Output>(path: Path, newValue: any, obj: object): Output

It makes a shallow clone of obj with setting or overriding with newValue the property found with path.

const path = 'b.c'
const newValue = 2
const obj = { a: 1 }

R.assocPath(path, newValue, Record<string, unknown>)
// => { a : 1, b : { c : 2 }}

Try this R.assocPath example in Rambda REPL

binary

Try this R.binary example in Rambda REPL

bind

bind<F extends AnyFunction, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>

Creates a function that is bound to a context.

:boom: R.bind does not provide the additional argument-binding capabilities of Function.prototype.bind.

const log = R.bind(console.log, console)
const result = R.pipe(
  R.assoc('a', 2), 
  R.tap(log), 
  R.assoc('a', 3)
)({a: 1}); 
// => result - `{a: 3}`
// => console log - `{a: 2}`

Try this R.bind example in Rambda REPL

both

both(pred1: Pred, pred2: Pred): Pred

It returns a function with input argument.

This function will return true, if both firstCondition and secondCondition return true when input is passed as their argument.

const firstCondition = x => x > 10
const secondCondition = x => x < 20
const fn = R.both(firstCondition, secondCondition)

const result = [fn(15), fn(30)]
// => [true, false]

Try this R.both example in Rambda REPL

call

Try this R.call example in Rambda REPL

chain

chain<T, U>(fn: (n: T) => U[], list: T[]): U[]

The method is also known as flatMap.

const duplicate = n => [ n, n ]
const list = [ 1, 2, 3 ]

const result = chain(duplicate, list)
// => [ 1, 1, 2, 2, 3, 3 ]

Try this R.chain example in Rambda REPL

clamp

Restrict a number input to be within min and max limits.

If input is bigger than max, then the result is max.

If input is smaller than min, then the result is min.

Try this R.clamp example in Rambda REPL

clone

It creates a deep copy of the input, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.

:boom: It doesn't work with very specific types, such as MongoDB's ObjectId.

Try this R.clone example in Rambda REPL

collectBy

Try this R.collectBy example in Rambda REPL

comparator

It returns a comparator function that can be used in sort method.

Try this R.comparator example in Rambda REPL

complement

It returns inverted version of origin function that accept input as argument.

The return value of inverted is the negative boolean value of origin(input).

Try this R.complement example in Rambda REPL

compose

It performs right-to-left function composition.

Try this R.compose example in Rambda REPL

composeWith

Try this R.composeWith example in Rambda REPL

concat

It returns a new string or array, which is the result of merging x and y.

Try this R.concat example in Rambda REPL

cond

It takes list with conditions and returns a new function fn that expects input as argument.

This function will start evaluating the conditions in order to find the first winner(order of conditions matter).

The winner is this condition, which left side returns true when input is its argument. Then the evaluation of the right side of the winner will be the final result.

If no winner is found, then fn returns undefined.

Try this R.cond example in Rambda REPL

converge

Accepts a converging function and a list of branching functions and returns a new function. When invoked, this new function is applied to some arguments, each branching function is applied to those same arguments. The results of each branching function are passed as arguments to the converging function to produce the return value.

:boom: Explanation is taken from Ramda documentation

Try this R.converge example in Rambda REPL

count

It counts how many times predicate function returns true, when supplied with iteration of list.

Try this R.count example in Rambda REPL

countBy

countBy<T extends unknown>(transformFn: (x: T) => any, list: T[]): Record<string, number>

It counts elements in a list after each instance of the input list is passed through transformFn function.

const list = [ 'a', 'A', 'b', 'B', 'c', 'C' ]

const result = countBy(R.toLower, list)
const expected = { a: 2, b: 2, c: 2 }
// => `result` is equal to `expected`

Try this R.countBy example in Rambda REPL

curry

It expects a function as input and returns its curried version.

Try this R.curry example in Rambda REPL

curryN

It returns a curried equivalent of the provided function, with the specified arity.

dec

It decrements a number.

Try this R.dec example in Rambda REPL

defaultTo

defaultTo<T>(defaultValue: T, input: T | null | undefined): T

It returns defaultValue, if all of inputArguments are undefined, null or NaN.

Else, it returns the first truthy inputArguments instance(from left to right).

:boom: Rambda's defaultTo accept indefinite number of arguments when non curried, i.e. R.defaultTo(2, foo, bar, baz).

R.defaultTo('foo', 'bar') // => 'bar'
R.defaultTo('foo', undefined) // => 'foo'

// Important - emtpy string is not falsy value(same as Ramda)
R.defaultTo('foo', '') // => 'foo'

Try this R.defaultTo example in Rambda REPL

descend

Try this R.descend example in Rambda REPL

difference

difference<T>(a: T[], b: T[]): T[]

It returns the uniq set of all elements in the first list a not contained in the second list b.

R.equals is used to determine equality.

const a = [ 1, 2, 3, 4 ]
const b = [ 3, 4, 5, 6 ]

const result = R.difference(a, b)
// => [ 1, 2 ]

Try this R.difference example in Rambda REPL

differenceWith

differenceWith<T1, T2>(
  pred: (a: T1, b: T2) => boolean,
  list1: T1[],
  list2: T2[],
): T1[]

const result = R.differenceWith(
  (a, b) => a.x === b.x,
  [{x: 1}, {x: 2}],
  [{x: 1}, {x: 3}]
)
// => [{x: 2}]

Try this R.differenceWith example in Rambda REPL

dissoc

It returns a new object that does not contain property prop.

Try this R.dissoc example in Rambda REPL

dissocPath

Try this R.dissocPath example in Rambda REPL

divide

Try this R.divide example in Rambda REPL

drop

drop<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from beginning of list or string input.

R.drop(2, ['foo', 'bar', 'baz']) // => ['baz']
R.drop(2, 'foobar')  // => 'obar'

Try this R.drop example in Rambda REPL

dropLast

dropLast<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from the end of list or string input.

R.dropLast(2, ['foo', 'bar', 'baz']) // => ['foo']
R.dropLast(2, 'foobar')  // => 'foob'

Try this R.dropLast example in Rambda REPL

dropLastWhile

Try this R.dropLastWhile example in Rambda REPL

dropRepeats

dropRepeats<T>(list: T[]): T[]

It removes any successive duplicates according to R.equals.

const result = R.dropRepeats([
  1, 
  1, 
  {a: 1}, 
  {a:1}, 
  1
])
// => [1, {a: 1}, 1]

Try this R.dropRepeats example in Rambda REPL

dropRepeatsBy

Try this R.dropRepeatsBy example in Rambda REPL

dropRepeatsWith

Try this R.dropRepeatsWith example in Rambda REPL

dropWhile

Try this R.dropWhile example in Rambda REPL

either

either(firstPredicate: Pred, secondPredicate: Pred): Pred

It returns a new predicate function from firstPredicate and secondPredicate inputs.

This predicate function will return true, if any of the two input predicates return true.

const firstPredicate = x => x > 10
const secondPredicate = x => x % 2 === 0
const predicate = R.either(firstPredicate, secondPredicate)

const result = [
  predicate(15),
  predicate(8),
  predicate(7),
]
// => [true, true, false]

Try this R.either example in Rambda REPL

empty

Try this R.empty example in Rambda REPL

endsWith

endsWith<T extends string>(question: T, str: string): boolean

When iterable is a string, then it behaves as String.prototype.endsWith. When iterable is a list, then it uses R.equals to determine if the target list ends in the same way as the given target.

const str = 'foo-bar'
const list = [{a:1}, {a:2}, {a:3}]

const result = [
  R.endsWith('bar', str),
  R.endsWith([{a:1}, {a:2}], list)
]
// => [true, true]

Try this R.endsWith example in Rambda REPL

eqBy

Try this R.eqBy example in Rambda REPL

eqProps

It returns true if property prop in obj1 is equal to property prop in obj2 according to R.equals.

Try this R.eqProps example in Rambda REPL

equals

equals<T>(x: T, y: T): boolean

It deeply compares x and y and returns true if they are equal.

:boom: It doesn't handle cyclical data structures and functions

R.equals(
  [1, {a:2}, [{b: 3}]],
  [1, {a:2}, [{b: 3}]]
) // => true

Try this R.equals example in Rambda REPL

evolve

evolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[]

It takes object or array of functions as set of rules. These rules are applied to the iterable input to produce the result.

:boom: Error handling of this method differs between Ramda and Rambda. Ramda for some wrong inputs returns result and for other - it returns one of the inputs. Rambda simply throws when inputs are not correct. Full details for this mismatch are listed in source/_snapshots/evolve.spec.js.snap file.

const rules = {
  foo : add(1),
  bar : add(-1),
}
const input = {
  a   : 1,
  foo : 2,
  bar : 3,
}
const result = evolve(rules, input)
const expected = {
  a   : 1,
  foo : 3,
  bar : 2,
})
// => `result` is equal to `expected`

Try this R.evolve example in Rambda REPL

F

F(): boolean

F() // => false

Try this R.F example in Rambda REPL

filter

filter<T>(predicate: Predicate<T>): (input: T[]) => T[]

It filters list or object input using a predicate function.

const list = [3, 4, 3, 2]
const listPredicate = x => x > 2

const object = {abc: 'fo', xyz: 'bar', baz: 'foo'}
const objectPredicate = (x, prop) => x.length + prop.length > 5

const result = [
  R.filter(listPredicate, list),
  R.filter(objectPredicate, object)
]
// => [ [3, 4], { xyz: 'bar', baz: 'foo'} ]

Try this R.filter example in Rambda REPL

find

find<T>(predicate: (x: T) => boolean, list: T[]): T | undefined

It returns the first element of list that satisfy the predicate.

If there is no such element, it returns undefined.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.find(predicate, list)
// => {foo: 1}

Try this R.find example in Rambda REPL

findIndex

findIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the first element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.findIndex(predicate, list)
// => 1

Try this R.findIndex example in Rambda REPL

findLast

findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined

It returns the last element of list satisfying the predicate function.

If there is no such element, then undefined is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLast(predicate, list)
// => {foo: 1}

Try this R.findLast example in Rambda REPL

findLastIndex

findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the last element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLastIndex(predicate, list)
// => 1

Try this R.findLastIndex example in Rambda REPL

flatten

flatten<T>(list: any[]): T[]

It deeply flattens an array.

const result = R.flatten([
  1, 
  2, 
  [3, 30, [300]], 
  [4]
])
// => [ 1, 2, 3, 30, 300, 4 ]

Try this R.flatten example in Rambda REPL

flip

It returns function which calls fn with exchanged first and second argument.

:boom: Rambda's flip will throw if the arity of the input function is greater or equal to 5.

Try this R.flip example in Rambda REPL

forEach

forEach<T>(fn: Iterator<T, void>, list: T[]): T[]

It applies iterable function over all members of list and returns list.

:boom: It works with objects, unlike Ramda.

const sideEffect = {}
const result = R.forEach(
  x => sideEffect[`foo${x}`] = x
)([1, 2])

sideEffect // => {foo1: 1, foo2: 2}
result // => [1, 2]

Try this R.forEach example in Rambda REPL

forEachObjIndexed

fromPairs

It transforms a listOfPairs to an object.

Try this R.fromPairs example in Rambda REPL

groupBy

It splits list according to a provided groupFn function and returns an object.

Try this R.groupBy example in Rambda REPL

groupWith

It returns separated version of list or string input, where separation is done with equality compareFn function.

Try this R.groupWith example in Rambda REPL

gt

Try this R.gt example in Rambda REPL

gte

Try this R.gte example in Rambda REPL

has

has<T>(prop: string, obj: T): boolean

It returns true if obj has property prop.

const obj = {a: 1}

const result = [
  R.has('a', Record<string, unknown>),
  R.has('b', Record<string, unknown>)
]
// => [true, false]

Try this R.has example in Rambda REPL

hasIn

Try this R.hasIn example in Rambda REPL

hasPath

hasPath<T>(
  path: string | string[],
  input: object
): boolean

It will return true, if input object has truthy path(calculated with R.path).

const path = 'a.b'
const pathAsArray = ['a', 'b']
const obj = {a: {b: []}}

const result = [
  R.hasPath(path, Record<string, unknown>),
  R.hasPath(pathAsArray, Record<string, unknown>),
  R.hasPath('a.c', Record<string, unknown>),
]
// => [true, true, false]

Try this R.hasPath example in Rambda REPL

head

head(str: string): string

It returns the first element of list or string input. It returns undefined if array has length of 0.

const result = [
  R.head([1, 2, 3]),
  R.head('foo') 
]
// => [1, 'f']

Try this R.head example in Rambda REPL

identical

It returns true if its arguments a and b are identical.

Otherwise, it returns false.

:boom: Values are identical if they reference the same memory. NaN is identical to NaN; 0 and -0 are not identical.

Try this R.identical example in Rambda REPL

identity

identity<T>(input: T): T

It just passes back the supplied input argument.

:boom: Logic

R.identity(7) // => 7

Try this R.identity example in Rambda REPL

ifElse

ifElse<T, TFiltered extends T, TOnTrueResult, TOnFalseResult>(
  pred: (a: T) => a is TFiltered,
  onTrue: (a: TFiltered) => TOnTrueResult,
  onFalse: (a: Exclude<T, TFiltered>) => TOnFalseResult,
): (a: T) => TOnTrueResult | TOnFalseResult

It expects condition, onTrue and onFalse functions as inputs and it returns a new function with example name of fn.

When fn`` is called withinputargument, it will return eitheronTrue(input)oronFalse(input)depending oncondition(input)` evaluation.

const fn = R.ifElse(
 x => x>10,
 x => x*2,
 x => x*10
)

const result = [ fn(8), fn(18) ]
// => [80, 36]

Try this R.ifElse example in Rambda REPL

inc

It increments a number.

Try this R.inc example in Rambda REPL

includes

includes<T extends string>(valueToFind: T, input: string): boolean

If input is string, then this method work as native String.includes.

If input is array, then R.equals is used to define if valueToFind belongs to the list.

const result = [
  R.includes('oo', 'foo'),
  R.includes({a: 1}, [{a: 1}])
]
// => [true, true ]

Try this R.includes example in Rambda REPL

indexBy

It generates object with properties provided by condition and values provided by list array.

If condition is a function, then all list members are passed through it.

If condition is a string, then all list members are passed through R.path(condition).

Try this R.indexBy example in Rambda REPL

indexOf

It returns the index of the first element of list equals to valueToFind.

If there is no such element, it returns -1.

:boom: It uses R.equals for list of objects/arrays or native indexOf for any other case.

Try this R.indexOf example in Rambda REPL

init

init<T extends unknown[]>(input: T): T extends readonly [...infer U, any] ? U : [...T]

It returns all but the last element of list or string input.

const result = [
  R.init([1, 2, 3]) , 
  R.init('foo')  // => 'fo'
]
// => [[1, 2], 'fo']

Try this R.init example in Rambda REPL

innerJoin

It returns a new list by applying a predicate function to all elements of list1 and list2 and keeping only these elements where predicate returns true.

Try this R.innerJoin example in Rambda REPL

insert

Try this R.insert example in Rambda REPL

insertAll

Try this R.insertAll example in Rambda REPL

intersection

It loops through listA and listB and returns the intersection of the two according to R.equals.

:boom: There is slight difference between Rambda and Ramda implementation. Ramda.intersection(['a', 'b', 'c'], ['c', 'b']) result is "[ 'c', 'b' ]", but Rambda result is "[ 'b', 'c' ]".

Try this R.intersection example in Rambda REPL

intersperse

It adds a separator between members of list.

Try this R.intersperse example in Rambda REPL

is

It returns true if x is instance of targetPrototype.

Try this R.is example in Rambda REPL

isEmpty

isEmpty<T>(x: T): boolean

It returns true if x is empty.

const result = [
  R.isEmpty(''),
  R.isEmpty({ x : 0 })
]
// => [true, false]

Try this R.isEmpty example in Rambda REPL

isNil

isNil(x: any): x is null | undefined

It returns true if x is either null or undefined.

const result = [
  R.isNil(null),
  R.isNil(1),
]
// => [true, false]

Try this R.isNil example in Rambda REPL

isNotEmpty

isNotEmpty<T>(value: T[]): value is NonEmptyArray<T>

isNotNil

Try this R.isNotNil example in Rambda REPL

join

join<T>(glue: string, list: T[]): string

It returns a string of all list instances joined with a glue.

R.join('-', [1, 2, 3])  // => '1-2-3'

Try this R.join example in Rambda REPL

juxt

juxt<A extends any[], R1>(fns: [(...a: A) => R1]): (...a: A) => [R1]

It applies list of function to a list of inputs.

const getRange = juxt([ Math.min, Math.max, Math.min ])
const result = getRange(
  3, 4, 9, -3
)
// => [-3, 9, -3]

Try this R.juxt example in Rambda REPL

keys

keys<T extends object>(x: T): (keyof T & string)[]

It applies Object.keys over x and returns its keys.

R.keys({a:1, b:2})  // => ['a', 'b']

Try this R.keys example in Rambda REPL

last

last(str: ''): undefined

It returns the last element of input, as the input can be either a string or an array. It returns undefined if array has length of 0.

const result = [
  R.last([1, 2, 3]),
  R.last('foo'),
]
// => [3, 'o']

Try this R.last example in Rambda REPL

lastIndexOf

lastIndexOf<T>(target: T, list: T[]): number

It returns the last index of target in list array.

R.equals is used to determine equality between target and members of list.

If there is no such index, then -1 is returned.

const list = [1, 2, 3, 1, 2, 3]
const result = [
  R.lastIndexOf(2, list),
  R.lastIndexOf(4, list),
]
// => [4, -1]

Try this R.lastIndexOf example in Rambda REPL

length

length<T>(input: T[]): number

It returns the length property of list or string input.

const result = [
  R.length([1, 2, 3, 4]),
  R.length('foo'),
]
// => [4, 3]

Try this R.length example in Rambda REPL

lens

lens<S, A>(getter: (s: S) => A, setter: (a: A, s: S) => S): Lens<S, A>

It returns a lens for the given getter and setter functions.

The getter gets the value of the focus; the setter sets the value of the focus.

The setter should not mutate the data structure.

const xLens = R.lens(R.prop('x'), R.assoc('x'));

R.view(xLens, {x: 1, y: 2}) // => 1
R.set(xLens, 4, {x: 1, y: 2}) // => {x: 4, y: 2}
R.over(xLens, R.negate, {x: 1, y: 2}) // => {x: -1, y: 2}

Try this R.lens example in Rambda REPL

lensIndex

lensIndex<A>(n: number): Lens<A[], A>

It returns a lens that focuses on specified index.

const list = ['a', 'b', 'c']
const headLens = R.lensIndex(0)

R.view(headLens, list) // => 'a'
R.set(headLens, 'x', list) // => ['x', 'b', 'c']
R.over(headLens, R.toUpper, list) // => ['A', 'b', 'c']

Try this R.lensIndex example in Rambda REPL

lensPath

It returns a lens that focuses on specified path.

Try this R.lensPath example in Rambda REPL

lensProp

lensProp<S, K extends keyof S = keyof S>(prop: K): Lens<S, S[K]>

It returns a lens that focuses on specified property prop.

const xLens = R.lensProp('x');
const input = {x: 1, y: 2}

R.view(xLens, input) // => 1

R.set(xLens, 4, input) 
// => {x: 4, y: 2}

R.over(xLens, R.negate, input) 
// => {x: -1, y: 2}

Try this R.lensProp example in Rambda REPL

lt

Try this R.lt example in Rambda REPL

lte

Try this R.lte example in Rambda REPL

map

map<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>

It returns the result of looping through iterable with fn.

It works with both array and object.

:boom: Unlike Ramda's map, here property and input object are passed as arguments to fn, when iterable is an object.

const fn = x => x * 2
const fnWhenObject = (val, prop)=>{
  return `${prop}-${val}`
}

const iterable = [1, 2]
const obj = {a: 1, b: 2}

const result = [ 
  R.map(fn, list),
  R.map(fnWhenObject, Record<string, unknown>)
]
// => [ [1, 4], {a: 'a-1', b: 'b-2'}]

Try this R.map example in Rambda REPL

mapObjIndexed<T>(fn: ObjectIterator<T, T>, iterable: Dictionary<T>): Dictionary<T>

const fn = (val, prop) => {
  return `${prop}-${val}`
}

const obj = {a: 1, b: 2}

const result = R.map(mapObjIndexed, Record<string, unknown>)
// => {a: 'a-1', b: 'b-2'}

match(regExpression: RegExp, str: string): string[]

const result = [
  R.match('a', 'foo'),
  R.match(/([a-z]a)/g, 'bananas')
]
// => [[], ['ba', 'na', 'na']]

mean(list: number[]): number

R.mean([ 2, 7 ])
// => 4.5

median(list: number[]): number

R.median([ 7, 2, 10, 9 ]) // => 8

mergeAll<T>(list: object[]): T

const list = [
  {a: 1},
  {b: 2},
  {c: 3}
]
const result = R.mergeAll(list)
const expected = {
  a: 1,
  b: 2,
  c: 3
}
// => `result` is equal to `expected`

mergeDeepRight<Output>(target: object, newProps: object): Output

mergeLeft<Output>(newProps: object, target: object): Output

const result = R.mergeLeft(
  {a: 10},
  {a: 1, b: 2}
)
// => {a:10, b: 2}

mergeWith(fn: (x: any, z: any) => any, a: Record<string, unknown>, b: Record<string, unknown>): Record<string, unknown>

const result = R.mergeWith(
  R.concat,
  {values : [ 10, 20 ]},
  {values : [ 15, 35 ]}
)
// => [ 10, 20, 15, 35 ]

modify<K extends PropertyKey, T>(prop: K, fn: (value: T) => T): <U extends Record<K, T>>(object: U) => U

const result = R.modify()
// =>

none<T>(predicate: (x: T) => boolean, list: T[]): boolean

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > 6

const result = R.none(predicate, arr)
// => true

not(input: any): boolean

R.not(false) // true

nth(index: number, input: string): string

const list = [1, 2, 3]
const str = 'foo'

const result = [
  R.nth(2, list),
  R.nth(6, list),
  R.nth(0, str),
]
// => [3, undefined, 'f']

of<T>(x: T): T[]

R.of(null); // => [null]
R.of([42]); // => [[42]]

omit<T, K extends string>(propsToOmit: K[], obj: T): Omit<T, K>

const obj = {a: 1, b: 2, c: 3}
const propsToOmit = 'a,c,d'
const propsToOmitList = ['a', 'c', 'd']

const result = [
  R.omit(propsToOmit, Record<string, unknown>), 
  R.omit(propsToOmitList, Record<string, unknown>) 
]
// => [{b: 2}, {b: 2}]

once<T extends AnyFunction, C = unknown>(fn: T, context?: C): T

let result = 0
const addOnce = R.once((x) => result = result + x)

addOnce(1)
addOnce(1)
// => 1

over<S, A>(lens: Lens<S, A>): {
  (fn: (a: A) => A): (value: S) => S

const headLens = R.lensIndex(0)

R.over(headLens, R.toUpper, ['foo', 'bar', 'baz']) // => ['FOO', 'bar', 'baz']

partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T

const fn = (title, firstName, lastName) => {
  return title + ' ' + firstName + ' ' + lastName + '!'
}

const canPassAnyNumberOfArguments = R.partial(fn, 'Hello')
const ramdaStyle = R.partial(fn, ['Hello'])

const finalFn = canPassAnyNumberOfArguments('Foo')

finalFn('Bar') // =>  'Hello, Foo Bar!'

partialObject<Input, PartialInput, Output>(
  fn: (input: Input) => Output, 
  partialInput: PartialInput,
): (input: Pick<Input, Exclude<keyof Input, keyof PartialInput>>) => Output

const fn = ({ a, b, c }) => a + b + c
const curried = R.partialObject(fn, { a : 1 })
const result = curried({
  b : 2,
  c : 3,
})
// => 6

partition<T>(
  predicate: Predicate<T>,
  input: T[]
): [T[], T[]]

const list = [1, 2, 3]
const obj = {a: 1, b: 2, c: 3}
const predicate = x => x > 2

const result = [
  R.partition(predicate, list),
  R.partition(predicate, Record<string, unknown>)
]
const expected = [
  [[3], [1, 2]],
  [{c: 3},  {a: 1, b: 2}],
]
// `result` is equal to `expected`

path<S, K0 extends keyof S = keyof S>(path: [K0], obj: S): S[K0]

const obj = {a: {b: 1}}
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const result = [
  R.path(pathToSearch, Record<string, unknown>),
  R.path(pathToSearchList, Record<string, unknown>),
  R.path('a.b.c.d', Record<string, unknown>)
]
// => [1, 1, undefined]

pathEq(pathToSearch: Path, target: any, input: any): boolean

const path = 'a.b'
const target = {c: 1}
const input = {a: {b: {c: 1}}}

const result = R.pathEq(
  path,
  target,
  input
)
// => true

pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T

const defaultValue = 'DEFAULT_VALUE'
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const obj = {
  a : {
    b : 1
  }
}

const result = [
  R.pathOr(DEFAULT_VALUE, pathToSearch, Record<string, unknown>),
  R.pathOr(DEFAULT_VALUE, pathToSearchList, Record<string, unknown>), 
  R.pathOr(DEFAULT_VALUE, 'a.b.c', Record<string, unknown>)
]
// => [1, 1, 'DEFAULT_VALUE']

paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[]

const obj = {
  a : {
    b : {
      c : 1,
      d : 2
    }
  }
}

const result = R.paths([
  'a.b.c',
  'a.b.d',
  'a.b.c.d.e',
], Record<string, unknown>)
// => [1, 2, undefined]

pick<T, K extends string | number | symbol>(propsToPick: K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const list = [1, 2, 3, 4]
const propsToPick = 'a,foo'
const propsToPickList = ['a', 'foo']

const result = [
  R.pick(propsToPick, Record<string, unknown>),
  R.pick(propsToPickList, Record<string, unknown>),
  R.pick('a,bar', Record<string, unknown>),
  R.pick('bar', Record<string, unknown>),
  R.pick([0, 3, 5], list),
  R.pick('0,3,5', list),
]

const expected = [
  {a:1, foo: 'cherry'},
  {a:1, foo: 'cherry'},
  {a:1},
  {},
  {0: 1, 3: 4},
  {0: 1, 3: 4},
]
// => `result` is equal to `expected`

pickAll<T, K extends keyof T>(propsToPicks: K[], input: T): Pick<T, K>

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const propsToPick = 'a,foo,bar'
const propsToPickList = ['a', 'foo', 'bar']

const result = [
  R.pickAll(propsToPick, Record<string, unknown>),
  R.pickAll(propsToPickList, Record<string, unknown>),
  R.pickAll('a,bar', Record<string, unknown>),
  R.pickAll('bar', Record<string, unknown>),
]
const expected = [
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, bar: undefined},
  {bar: undefined}
]
// => `result` is equal to `expected`

pluck<K extends keyof T, T>(property: K, list: T[]): T[K][]

const list = [{a: 1}, {a: 2}, {b: 3}]
const property = 'a'

const result = R.pluck(property, list) 
// => [1, 2]

prepend<T>(xToPrepend: T, iterable: T[]): T[]

const result = R.prepend('foo', ['bar', 'baz'])
// => ['foo', 'bar', 'baz']

product(list: number[]): number

R.product([ 2, 3, 4 ])
// => 24)

prop<_, P extends keyof never, T>(p: P, value: T): Prop<T, P>

const result = [
  R.prop('x', {x: 100}), 
  R.prop('x', {a: 1}) 
]
// => [100, undefined]

propEq<K extends string | number>(valueToMatch: any, propToFind: K, obj: Record<K, any>): boolean

const obj = { foo: 'bar' }
const secondObj = { foo: 1 }

const propToFind = 'foo'
const valueToMatch = 'bar'

const result = [
  R.propEq(propToFind, valueToMatch, Record<string, unknown>),
  R.propEq(propToFind, valueToMatch, secondRecord<string, unknown>)
]
// => [true, false]

propIs<C extends AnyFunction, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, ReturnType<C>>

const obj = {a:1, b: 'foo'}

const result = [
  R.propIs(Number, 'a', Record<string, unknown>),
  R.propIs(String, 'b', Record<string, unknown>),
  R.propIs(Number, 'b', Record<string, unknown>),
]
// => [true, true, false]

propOr<T, P extends string>(defaultValue: T, property: P, obj: Partial<Record<P, T>> | undefined): T

const obj = {a: 1}
const defaultValue = 'DEFAULT_VALUE'
const property = 'a'

const result = [
  R.propOr(defaultValue, property, Record<string, unknown>),
  R.propOr(defaultValue, 'foo', Record<string, unknown>)
]
// => [1, 'DEFAULT_VALUE']

props<P extends string, T>(propsToPick: P[], obj: Record<P, T>): T[]

const result = R.props(
  ['a', 'b'], 
  {a:1, c:3}
)
// => [1, undefined]

propSatisfies<T>(predicate: Predicate<T>, property: string, obj: Record<string, T>): boolean

const obj = {a: {b:1}}
const property = 'a'
const predicate = x => x?.b === 1

const result = R.propSatisfies(predicate, property, Record<string, unknown>)
// => true

range(startInclusive: number, endExclusive: number): number[]

R.range(0, 5)
// => [0, 1, 2, 3, 4]

reject<T>(predicate: Predicate<T>, list: T[]): T[]

const list = [1, 2, 3, 4]
const obj = {a: 1, b: 2}
const predicate = x => x > 1

const result = [
  R.reject(predicate, list),
  R.reject(predicate, Record<string, unknown>)
]
// => [[1], {a: 1}]

removeIndex<T>(index: number, list: T[]): T[]

const list = [1, 2, 3, 4]
const result = R.removeIndex(1, list)
// => [1, 3, 4]

repeat<T>(x: T): (timesToRepeat: number) => T[]

R.repeat('foo', 3)
// => ['foo', 'foo', 'foo']

replace(strOrRegex: RegExp | string, replacer: RegExpReplacer, str: string): string

const strOrRegex = /o/g

const result = R.replace(strOrRegex, '|0|', 'foo')
// => 'f|0||0|'

reverse<T>(input: T[]): T[]

const result = [
  R.reverse('foo'),
  R.reverse([1, 2, 3])
]
// => ['oof', [3, 2, 1]

set<S, A>(lens: Lens<S, A>): {
  (a: A): (obj: S) => S
  (a: A, obj: S): S
}

const input = {x: 1, y: 2}
const xLens = R.lensProp('x')

const result = [
  R.set(xLens, 4, input),
  R.set(xLens, 8, input) 
]
// => [{x: 4, y: 2}, {x: 8, y: 2}]

slice(from: number, to: number, input: string): string

const list = [0, 1, 2, 3, 4, 5]
const str = 'FOO_BAR'
const from = 1
const to = 4

const result = [
  R.slice(from, to, str),
  R.slice(from, to, list)
]
// => ['OO_', [1, 2, 3]]

sort<T>(sortFn: (a: T, b: T) => number, list: T[]): T[]

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = (x, y) => {
  return x.a > y.a ? 1 : -1
}

const result = R.sort(sortFn, list)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

sortBy<T>(sortFn: (a: T) => Ord, list: T[]): T[]

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = x => x.a

const result = R.sortBy(sortFn, list)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

split(separator: string | RegExp): (str: string) => string[]

const str = 'foo|bar|baz'
const separator = '|'
const result = R.split(separator, str)
// => [ 'foo', 'bar', 'baz' ]

splitAt<T>(index: number, input: T[]): [T[], T[]]

const list = [ 1, 2, 3 ]
const result = R.splitAt(2, list)
// => [[ 1, 2 ], [ 3 ]]

splitEvery<T>(sliceLength: number, input: T[]): (T[])[]

const result = [
  R.splitEvery(2, [1, 2, 3]), 
  R.splitEvery(3, 'foobar') 
]

const expected = [
  [[1, 2], [3]],
  ['foo', 'bar']
]
// => `result` is equal to `expected`

splitWhen<T, U>(predicate: Predicate<T>, list: U[]): (U[])[]

const list = [1, 2, 1, 2]
const result = R.splitWhen(R.equals(2), list)
// => [[1], [2, 1, 2]]

startsWith<T extends string>(question: T, input: string): boolean

const str = 'foo-bar'
const list = [{a:1}, {a:2}, {a:3}]

const result = [
  R.startsWith('foo', str),
  R.startsWith([{a:1}, {a:2}], list)
]
// => [true, true]

sum(list: number[]): number

R.sum([1, 2, 3, 4, 5]) 
// => 15

symmetricDifference<T>(x: T[], y: T[]): T[]

const x = [ 1, 2, 3, 4 ]
const y = [ 3, 4, 5, 6 ]

const result = R.symmetricDifference(x, y)
// => [ 1, 2, 5, 6 ]

T(): boolean

R.T() 
// => true

tail<T extends unknown[]>(input: T): T extends [any, ...infer U] ? U : [...T]

const result = [
  R.tail([1, 2, 3]),  
  R.tail('foo') 
]
// => [[2, 3], 'oo']

take<T>(howMany: number, input: T[]): T[]

const howMany = 2

const result = [
  R.take(howMany, [1, 2, 3]),
  R.take(howMany, 'foobar'),
]
// => [[1, 2], 'fo']

takeLast<T>(howMany: number, input: T[]): T[]

const howMany = 2

const result = [
  R.takeLast(howMany, [1, 2, 3]),
  R.takeLast(howMany, 'foobar'),
]
// => [[2, 3], 'ar']

takeLastWhile(predicate: (x: string) => boolean, input: string): string

const result = R.takeLastWhile(
  x => x > 2,
  [1, 2, 3, 4]
)
// => [3, 4]

tap<T>(fn: (x: T) => void, input: T): T

const list = [1, 2, 3]

R.compose(
  R.map(x => x * 2)
  R.tap(console.log),
  R.filter(x => x > 1)
)(list)
// => `2` and `3` will be logged

test(regExpression: RegExp): (str: string) => boolean

R.test(/^f/, 'foo')
// => true

times<T>(fn: (i: number) => T, howMany: number): T[]

const fn = x => x * 2
const howMany = 5

R.times(fn, howMany)
// => [0, 2, 4, 6, 8]

toLower<S extends string>(str: S): Lowercase<S>

R.toLower('FOO')
// => 'foo'

toPairs<O extends object, K extends Extract<keyof O, string | number>>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>

const list = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ] ]

const result = R.toPairs(list)
// => `result` is equal to `expected`

toString(x: unknown): string

R.toString([1, 2]) 
// => '1,2'

toUpper<S extends string>(str: S): Uppercase<S>

R.toUpper('foo')
// => 'FOO'

transpose<T>(list: (T[])[]): (T[])[]

const list = [[10, 11], [20], [], [30, 31, 32]]
const expected = [[10, 20, 30], [11, 31], [32]]

const result = R.transpose(list)
// => `result` is equal to `expected`

trim(str: string): string

R.trim('  foo  ') 
// => 'foo'

unapply<T = any>(fn: (args: any[]) => T): (...args: any[]) => T

R.unapply(JSON.stringify)(1, 2, 3)
//=> '[1,2,3]'

union<T>(x: T[], y: T[]): T[]

const result = R.union([1,2,3], [3,4,5]);
// => [1, 2, 3, 4, 5]

uniq<T>(list: T[]): T[]

const list = [1, 1, {a: 1}, {a: 2}, {a:1}]

R.uniq(list)
// => [1, {a: 1}, {a: 2}]

uniqWith<T, U>(predicate: (x: T, y: T) => boolean, list: T[]): T[]

const list = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
  {id: 3, title:'foo'},
  {id: 4, title:'bar'},
]

const expected = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
]

const predicate = (x,y) => x.title === y.title

const result = R.uniqWith(predicate, list)
// => `result` is equal to `expected`

unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U

const fn = R.unless(
  x => x > 2,
  x => x + 10
)

const result = [
  fn(1),
  fn(5)
]
// => [11, 5]

update<T>(index: number, newValue: T, list: T[]): T[]

const index = 2
const newValue = 88
const list = [1, 2, 3, 4, 5]

const result = R.update(index, newValue, list)
// => [1, 2, 88, 4, 5]

values<T extends object, K extends keyof T>(obj: T): T[K][]

const obj = {a:1, b:2}

R.values(Record<string, unknown>)
// => [1, 2]

view<S, A>(lens: Lens<S, A>): (obj: S) => A

const lens = R.lensProp('x')

R.view(lens, {x: 1, y: 2}) // => 1
R.view(lens, {x: 4, y: 2}) // => 4

when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U

const predicate = x => typeof x === 'number'
const whenTrueFn = R.add(11)

const fn = when(predicate, whenTrueResult)

const positiveInput = 88
const negativeInput = 'foo'

const result = [
  fn(positiveInput),
  fn(positiveInput),
]

const expected = [
  99,
  'foo',
]
// => `result` is equal to `expected`

where<T, U>(conditions: T, input: U): boolean

const condition = R.where({
  a : x => typeof x === "string",
  b : x => x === 4
})
const input = {
  a : "foo",
  b : 4,
  c : 11,
}

const result = condition(input) 
// => true

whereEq<T, U>(condition: T, input: U): boolean

const condition = { a : { b : 1 } }
const input = {
  a : { b : 1 },
  c : 2
}

const result = whereEq(condition, input)
// => true

without<T>(matchAgainst: T[], source: T[]): T[]

const source = [1, 2, 3, 4]
const matchAgainst = [2, 3]

const result = R.without(matchAgainst, source)
// => [1, 4]

xor(x: boolean, y: boolean): boolean

const result = [
  xor(true, true),
  xor(false, false),
  xor(false, true),
]
// => [false, false, true]

zip<K, V>(x: K[], y: V[]): KeyValuePair<K, V>[]

const x = [1, 2]
const y = ['A', 'B']
R.zip(x, y)
// => [[1, 'A'], [2, 'B']]

// truncates to shortest list
R.zip([...x, 3], ['A', 'B'])
// => [[1, 'A'], [2, 'B']]

zipObj<T, K extends string>(keys: K[], values: T[]): { [P in K]: T }

const keys = ['a', 'b', 'c']

R.zipObj(keys, [1, 2, 3])
// => {a: 1, b: 2, c: 3}

// truncates to shortest list
R.zipObj(keys, [1, 2])
// => {a: 1, b: 2}

zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[]

const list1 = [ 10, 20, 30, 40 ]
const list2 = [ 100, 200 ]

const result = R.zipWith(
  R.add, list1, list2
)
// => [110, 220]