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Record overview

The Record module enables dealing with Typescript’s Record<K, T> type in a functional way, basically treating it as a Functor in T.

Added in v2.0.0


Table of contents


Compactable

compact

Compact a Record of Options discarding the None values and keeping the Some values.

Signature

export declare const compact: <A>(fa: Record<string, Option<A>>) => Record<string, A>

Example

import { compact } from 'fp-ts/Record'
import { option } from 'fp-ts'

assert.deepStrictEqual(compact({ a: option.some('foo'), b: option.none, c: option.some('bar') }), {
  a: 'foo',
  c: 'bar',
})

Added in v2.0.0

separate

Separate a Record of Eithers into Lefts and Rights.

Signature

export declare const separate: <A, B>(
  fa: Record<string, Either<A, B>>
) => Separated<Record<string, A>, Record<string, B>>

Example

import { separate } from 'fp-ts/Record'
import { either } from 'fp-ts'

assert.deepStrictEqual(separate({ a: either.right('foo'), b: either.left('bar'), c: either.right('baz') }), {
  right: {
    a: 'foo',
    c: 'baz',
  },
  left: {
    b: 'bar',
  },
})

Added in v2.0.0

Filterable

filter

Given a Predicate, it produces a new Record keeping only the entries with a value that satisfies the provided predicate.

Signature

export declare const filter: {
  <A, B extends A>(refinement: Refinement<A, B>): (fa: Record<string, A>) => Record<string, B>
  <A>(predicate: Predicate<A>): <B extends A>(fb: Record<string, B>) => Record<string, B>
  <A>(predicate: Predicate<A>): (fa: Record<string, A>) => Record<string, A>
}

Example

import { filter } from 'fp-ts/Record'

assert.deepStrictEqual(filter((s: string) => s.length < 4)({ a: 'foo', b: 'bar', c: 'verylong' }), {
  a: 'foo',
  b: 'bar',
})

Added in v2.0.0

filterMap

Maps a Record with an iterating function that returns an Option and it keeps only the Some values discarding the Nones.

Signature

export declare const filterMap: <A, B>(f: (a: A) => Option<B>) => (fa: Record<string, A>) => Record<string, B>

Example

import { filterMap } from 'fp-ts/Record'
import { option } from 'fp-ts'

const f = (s: string) => (s.length < 4 ? option.some(`${s} is short`) : option.none)
assert.deepStrictEqual(filterMap(f)({ a: 'foo', b: 'bar', c: 'verylong' }), {
  a: 'foo is short',
  b: 'bar is short',
})

Added in v2.0.0

partition

Partition a Record into two parts according to a Predicate.

Signature

export declare const partition: {
  <A, B extends A>(refinement: Refinement<A, B>): (
    fa: Record<string, A>
  ) => Separated<Record<string, A>, Record<string, B>>
  <A>(predicate: Predicate<A>): <B extends A>(fb: Record<string, B>) => Separated<Record<string, B>, Record<string, B>>
  <A>(predicate: Predicate<A>): (fa: Record<string, A>) => Separated<Record<string, A>, Record<string, A>>
}

Example

import { partition } from 'fp-ts/Record'

assert.deepStrictEqual(partition((s: string) => s.length < 4)({ a: 'foo', b: 'bar', c: 'verylong' }), {
  left: {
    c: 'verylong',
  },
  right: {
    a: 'foo',
    b: 'bar',
  },
})

Added in v2.0.0

partitionMap

Maps a Record with a function returning an Either and partitions the resulting Record into Lefts and Rights.

Signature

export declare const partitionMap: <A, B, C>(
  f: (a: A) => Either<B, C>
) => (fa: Record<string, A>) => Separated<Record<string, B>, Record<string, C>>

Example

import { partitionMap } from 'fp-ts/Record'
import { either } from 'fp-ts'

const f = (s: string) => (s.length < 4 ? either.right(`${s} is short`) : either.left(`${s} is not short`))
assert.deepStrictEqual(partitionMap(f)({ a: 'foo', b: 'bar', c: 'verylong' }), {
  left: {
    c: 'verylong is not short',
  },
  right: {
    a: 'foo is short',
    b: 'bar is short',
  },
})

Added in v2.0.0

Foldable

foldMap

Map and fold a Record. Map the Record passing each value to the iterating function. Then fold the results using the provided Monoid.

Signature

export declare function foldMap(
  O: Ord<string>
): <M>(M: Monoid<M>) => <A>(f: (a: A) => M) => (fa: Record<string, A>) => M
export declare function foldMap<M>(M: Monoid<M>): <A>(f: (a: A) => M) => (fa: Record<string, A>) => M

Example

import { foldMap } from 'fp-ts/Record'
import { Ord } from 'fp-ts/string'
import { Monoid } from 'fp-ts/Monoid'

const m: Monoid<string> = { empty: '', concat: (x: string, y: string) => (x ? `${x} -> ${y}` : `${y}`) }
const f = (a: number) => `-${a}-`
const x = { c: 3, a: 1, b: 2 }
assert.deepStrictEqual(foldMap(Ord)(m)(f)(x), '-1- -> -2- -> -3-')

Added in v2.0.0

reduce

Reduces a Record passing each value to the iterating function. Entries are processed in order, sorted by key according to the given Ord.

Signature

export declare function reduce(O: Ord<string>): <A, B>(b: B, f: (b: B, a: A) => B) => (fa: Record<string, A>) => B
export declare function reduce<A, B>(b: B, f: (b: B, a: A) => B): (fa: Record<string, A>) => B

Example

import { reduce } from 'fp-ts/Record'
import { Ord } from 'fp-ts/string'

const x = { c: 3, a: 'foo', b: false }
assert.deepStrictEqual(reduce(Ord)([] as string[], (b, a) => [...b, `-${a}-`])(x), ['-foo-', '-false-', '-3-'])

Added in v2.0.0

reduceRight

Same as reduce but entries are processed from the right, i.e. in reverse order, from the last to the first entry, according to the given Ord.

Signature

export declare function reduceRight(O: Ord<string>): <A, B>(b: B, f: (a: A, b: B) => B) => (fa: Record<string, A>) => B
export declare function reduceRight<A, B>(b: B, f: (a: A, b: B) => B): (fa: Record<string, A>) => B

Example

import { reduceRight } from 'fp-ts/Record'
import { Ord } from 'fp-ts/string'

const x = { c: 3, a: 'foo', b: false }
assert.deepStrictEqual(reduceRight(Ord)([] as string[], (a, b) => [...b, `-${a}-`])(x), ['-3-', '-false-', '-foo-'])

Added in v2.0.0

Witherable

wilt

Signature

export declare const wilt: PipeableWilt1<'Record'>

Added in v2.6.5

wither

Signature

export declare const wither: PipeableWither1<'Record'>

Added in v2.6.5

combinators

difference

Difference between two Records. Takes two Records and produces a Record composed by the entries of the two inputs, removing the entries with the same key in both inputs.

Signature

export declare const difference: <A>(second: Record<string, A>) => (first: Record<string, A>) => Record<string, A>

Example

import { difference } from 'fp-ts/Record'

assert.deepStrictEqual(difference({ a: 1 })({ a: 1, b: 2 }), { b: 2 })
assert.deepStrictEqual(difference({ a: 3 })({ a: 1, b: 2 }), { b: 2 })
assert.deepStrictEqual(difference({ a: 3, c: 3 })({ a: 1, b: 2 }), { b: 2, c: 3 })

Added in v2.11.0

flap

Derivable from Functor. Takes a value and a Record of functions and returns a Record by applying each function to the input value.

Signature

export declare const flap: <A>(a: A) => <B>(fab: Record<string, (a: A) => B>) => Record<string, B>

Example

import { flap } from 'fp-ts/Record'

const fab = { x: (n: number) => `${n} times 2`, y: (n: number) => `${n * 2}` }
assert.deepStrictEqual(flap(3)(fab), {
  x: '3 times 2',
  y: '6',
})

Added in v2.10.0

intersection

Intersection of two Records. Takes two Records and produces a Record combining only the entries of the two inputswith the same key. It uses the concat function of the provided Magma to combine the elements.

Signature

export declare const intersection: <A>(
  M: Magma<A>
) => (second: Record<string, A>) => (first: Record<string, A>) => Record<string, A>

Example

import { intersection } from 'fp-ts/Record'
import { Magma } from 'fp-ts/Magma'

const m1: Magma<number> = { concat: (x: number, y: number) => x + y }
assert.deepStrictEqual(intersection(m1)({ a: 3, c: 3 })({ a: 1, b: 2 }), { a: 4 })
const m2: Magma<number> = { concat: (x: number) => x }
assert.deepStrictEqual(intersection(m2)({ a: 3, c: 3 })({ a: 1, b: 2 }), { a: 1 })

Added in v2.11.0

union

Union of two Records. Takes two Records and produces a Record combining all the entries of the two inputs. It uses the concat function of the provided Magma to combine the elements with the same key.

Signature

export declare const union: <A>(
  M: Magma<A>
) => (second: Record<string, A>) => (first: Record<string, A>) => Record<string, A>

Example

import { union } from 'fp-ts/Record'
import { Magma } from 'fp-ts/Magma'

const m1: Magma<number> = { concat: (x: number, y: number) => x + y }
assert.deepStrictEqual(union(m1)({ a: 3, c: 3 })({ a: 1, b: 2 }), { a: 4, b: 2, c: 3 })
const m2: Magma<number> = { concat: (x: number) => x }
assert.deepStrictEqual(union(m2)({ a: 3, c: 3 })({ a: 1, b: 2 }), { a: 1, b: 2, c: 3 })

Added in v2.11.0

upsertAt

Insert or replace a key/value pair in a Record.

Signature

export declare const upsertAt: <A>(k: string, a: A) => (r: Record<string, A>) => Record<string, A>

Example

import { upsertAt } from 'fp-ts/Record'

assert.deepStrictEqual(upsertAt('a', 5)({ a: 1, b: 2 }), { a: 5, b: 2 })
assert.deepStrictEqual(upsertAt('c', 5)({ a: 1, b: 2 }), { a: 1, b: 2, c: 5 })

Added in v2.10.0

instances

Compactable

Signature

export declare const Compactable: Compactable1<'Record'>

Added in v2.7.0

Filterable

Signature

export declare const Filterable: Filterable1<'Record'>

Added in v2.7.0

FilterableWithIndex

Signature

export declare const FilterableWithIndex: FilterableWithIndex1<'Record', string>

Added in v2.7.0

Functor

Signature

export declare const Functor: Functor1<'Record'>

Added in v2.7.0

FunctorWithIndex

Signature

export declare const FunctorWithIndex: FunctorWithIndex1<'Record', string>

Added in v2.7.0

URI

Signature

export declare const URI: 'Record'

Added in v2.0.0

URI (type alias)

Signature

export type URI = typeof URI

Added in v2.0.0

getDifferenceMagma

Produces a Magma with a concat function that combines two Records by making the difference.

Signature

export declare const getDifferenceMagma: <A>() => Magma<Record<string, A>>

Example

import { getDifferenceMagma, difference } from 'fp-ts/Record'
import { Magma } from 'fp-ts/Magma'

const r1 = { a: 3, c: 3 }
const r2 = { a: 1, b: 2 }
const m: Magma<Record<string, number>> = getDifferenceMagma<number>()
assert.deepStrictEqual(m.concat(r1, r2), difference(r2)(r1))
assert.deepStrictEqual(m.concat(r1, r2), { c: 3, b: 2 })

Added in v2.11.0

getEq

Given an Eq for the base type, it produces an Eq for a Record of that base type.

Signature

export declare const getEq: <K extends string, A>(E: Eq<A>) => Eq<Record<K, A>>

Example

import { getEq } from 'fp-ts/Record'
import { string } from 'fp-ts'
import { Eq } from 'fp-ts/Eq'

const eq: Eq<Record<string, string>> = getEq(string.Eq)
assert.deepStrictEqual(eq.equals({ a: 'foo' }, { b: 'bar' }), false)
assert.deepStrictEqual(eq.equals({ a: 'foo' }, { a: 'foo' }), true)

Added in v2.0.0

getFoldable

Produces a Foldable instance for a Record, using the provided Ord to sort the Record’s entries by key.

Signature

export declare const getFoldable: (O: Ord<string>) => Foldable1<URI>

Added in v2.11.0

getFoldableWithIndex

Produces a FoldableWithIndex1 instance for a Record, using the provided Ord to sort the Record’s entries by key.

Signature

export declare const getFoldableWithIndex: (O: Ord<string>) => FoldableWithIndex1<URI, string>

Added in v2.11.0

getIntersectionSemigroup

Given a Semigroup in the base type, it produces a Semigroup in the Record of the base type. The resulting Semigroup concatenates two Records by intersection.

Signature

export declare const getIntersectionSemigroup: <A>(S: Semigroup<A>) => Semigroup<Record<string, A>>

Example

import { getIntersectionSemigroup } from 'fp-ts/Record'
import { Semigroup } from 'fp-ts/Semigroup'

const sNumber: Semigroup<number> = { concat: (x, y) => x - y }
const sRecord: Semigroup<Record<string, number>> = getIntersectionSemigroup(sNumber)
assert.deepStrictEqual(sRecord.concat({ a: 1, b: 2 }, { b: 3, c: 4 }), { b: -1 })

Added in v2.11.0

getMonoid

Returns a Monoid instance for Records, given a Semigroup instance for the base type. The Monoid makes the union of two Records comining the overlapping entries with the provided Semigroup.

Signature

export declare const getMonoid: <K extends string, A>(S: Semigroup<A>) => Monoid<Record<K, A>>

Example

import { SemigroupSum } from 'fp-ts/number'
import { getMonoid } from 'fp-ts/Record'

const M = getMonoid(SemigroupSum)
assert.deepStrictEqual(M.concat({ foo: 123, bar: 234 }, { foo: 456, baz: 567 }), { foo: 579, bar: 234, baz: 567 })

Added in v2.0.0

getShow

Produces a Show for a Record, given a Show for the base type (a Show produces a human-readable representation of an instance). Record entries are sorted by key with the provided Ord.

Signature

export declare function getShow(O: Ord<string>): <A>(S: Show<A>) => Show<Record<string, A>>
export declare function getShow<A>(S: Show<A>): Show<Record<string, A>>

Example

import { getShow } from 'fp-ts/Record'
import { Show } from 'fp-ts/Show'
import { Ord } from 'fp-ts/string'

const sNumber: Show<number> = { show: (n: number) => `${n}` }
const sRecord: Show<Record<string, number>> = getShow(Ord)(sNumber)
assert.deepStrictEqual(sRecord.show({ b: 2, a: 1 }), '{ "a": 1, "b": 2 }')

Added in v2.0.0

getTraversable

Produces a Traversable instance for a Record, using the provided Ord to sort the Record’s entries by key.

Signature

export declare const getTraversable: (O: Ord<string>) => Traversable1<URI>

Added in v2.11.0

getTraversableWithIndex

Produces a TraversableWithIndex instance for a Record, using the provided Ord to sort the Record’s entries by key.

Signature

export declare const getTraversableWithIndex: (O: Ord<string>) => TraversableWithIndex1<URI, string>

Added in v2.11.0

getUnionMonoid

Same as getMonoid. Returns a Monoid instance for Records given a Semigroup instance for the base type. The Monoid makes the union of two Records combining the entries that have the same key with the provided Semigroup.

Signature

export declare const getUnionMonoid: <A>(S: Semigroup<A>) => Monoid<Record<string, A>>

Example

import { SemigroupSum } from 'fp-ts/number'
import { getUnionMonoid } from 'fp-ts/Record'

const M = getUnionMonoid(SemigroupSum)
assert.deepStrictEqual(M.concat({ foo: 123, bar: 234 }, { foo: 456, baz: 567 }), { foo: 579, bar: 234, baz: 567 })

Added in v2.11.0

getUnionSemigroup

Given a Semigroup in the base type, it produces a Semigroup in the Record of the base type. The resulting Semigroup concatenates two Records by union.

Signature

export declare const getUnionSemigroup: <A>(S: Semigroup<A>) => Semigroup<Record<string, A>>

Example

import { getUnionSemigroup } from 'fp-ts/Record'
import { Semigroup } from 'fp-ts/Semigroup'

const sNumber: Semigroup<number> = { concat: (x, y) => x - y }
const sRecord: Semigroup<Record<string, number>> = getUnionSemigroup(sNumber)
assert.deepStrictEqual(sRecord.concat({ a: 1, b: 2 }, { b: 3, c: 4 }), { a: 1, b: -1, c: 4 })

Added in v2.11.0

getWitherable

Signature

export declare const getWitherable: (O: Ord<string>) => Witherable1<URI>

Added in v2.11.0

FoldableWithIndex

Use getFoldableWithIndex instead.

Signature

export declare const FoldableWithIndex: FoldableWithIndex1<'Record', string>

Added in v2.7.0

Foldable

Use getFoldable instead.

Signature

export declare const Foldable: Foldable1<'Record'>

Added in v2.7.0

TraversableWithIndex

Use the getTraversableWithIndex instead.

Signature

export declare const TraversableWithIndex: TraversableWithIndex1<'Record', string>

Added in v2.7.0

Traversable

Use getTraversable instead.

Signature

export declare const Traversable: Traversable1<'Record'>

Added in v2.7.0

Witherable

Use getWitherable instead.

Signature

export declare const Witherable: Witherable1<'Record'>

Added in v2.7.0

record

Use small, specific instances instead.

Signature

export declare const record: FunctorWithIndex1<'Record', string> &
  FoldableWithIndex1<'Record', string> &
  FilterableWithIndex1<'Record', string> &
  TraversableWithIndex1<'Record', string> &
  Witherable1<'Record'>

Added in v2.0.0

utils

collect

Map a Record into an Array. It passes each key/value pair to the iterating function and collects the results in an array, sorted alphabetically by the original key.

Signature

export declare function collect(
  O: Ord<string>
): <K extends string, A, B>(f: (k: K, a: A) => B) => (r: Record<K, A>) => Array<B>
export declare function collect<K extends string, A, B>(f: (k: K, a: A) => B): (r: Record<K, A>) => Array<B>

Example

import { collect } from 'fp-ts/Record'
import { Ord } from 'fp-ts/string'

const f = <A>(k: string, a: A) => `${k.toUpperCase()}-${a}`
const x = { c: 3, a: 'foo', b: false }
assert.deepStrictEqual(collect(Ord)(f)(x), ['A-foo', 'B-false', 'C-3'])

Added in v2.0.0

deleteAt

Delete a key and value from a Record.

Signature

export declare function deleteAt<K extends string>(
  k: K
): <KS extends string, A>(r: Record<KS, A>) => Record<string extends K ? string : Exclude<KS, K>, A>

Example

import { deleteAt } from 'fp-ts/Record'

assert.deepStrictEqual(deleteAt('a')({ a: 1, b: 2 }), { b: 2 })
assert.deepStrictEqual(deleteAt('c')({ a: 1, b: 2 }), { a: 1, b: 2 })

Added in v2.0.0

elem

Given an Eq checks if a Record contains an entry with value equal to a provided value.

Signature

export declare const elem: <A>(
  E: Eq<A>
) => { (a: A): (fa: Record<string, A>) => boolean; (a: A, fa: Record<string, A>): boolean }

Example

import { elem } from 'fp-ts/Record'
import { number } from 'fp-ts'

assert.deepStrictEqual(elem(number.Eq)(123, { foo: 123, bar: 234 }), true)
assert.deepStrictEqual(elem(number.Eq)(-7, { foo: 123, bar: 234 }), false)

Added in v2.0.0

every

Test if every value in a Record satisfies the predicate.

Signature

export declare const every: <A>(predicate: Predicate<A>) => (r: Record<string, A>) => boolean

Example

import { every } from 'fp-ts/Record'

assert.deepStrictEqual(every((n: number) => n >= 0)({ a: 1, b: 2 }), true)
assert.deepStrictEqual(every((n: number) => n >= 0)({ a: 1, b: -1 }), false)

Added in v2.0.0

filterMapWithIndex

Maps a Record with an iterating function that takes key and value and returns an Option, keeping only the Some values and discarding Nones.

Signature

export declare const filterMapWithIndex: <K extends string, A, B>(
  f: (key: K, a: A) => Option<B>
) => (fa: Record<K, A>) => Record<string, B>

Example

import { filterMapWithIndex } from 'fp-ts/Record'
import { option } from 'fp-ts'

const f = (key: string, a: number) => (a >= 0 ? option.some(`${key}${a}`) : option.none)
assert.deepStrictEqual(filterMapWithIndex(f)({ a: -1, b: 2, c: 3 }), {
  b: 'b2',
  c: 'c3',
})

Added in v2.0.0

filterWithIndex

Produce a new Record keeping only the entries that satisfy a predicate taking key and value as input.

Signature

export declare function filterWithIndex<K extends string, A, B extends A>(
  refinementWithIndex: RefinementWithIndex<K, A, B>
): (fa: Record<K, A>) => Record<string, B>
export declare function filterWithIndex<K extends string, A>(
  predicateWithIndex: PredicateWithIndex<K, A>
): <B extends A>(fb: Record<K, B>) => Record<string, B>
export declare function filterWithIndex<K extends string, A>(
  predicateWithIndex: PredicateWithIndex<K, A>
): (fa: Record<K, A>) => Record<string, A>

Example

import { filterWithIndex } from 'fp-ts/Record'

assert.deepStrictEqual(filterWithIndex((s: string, v: number) => s.length <= 1 && v > 0)({ a: 1, b: -2, ccc: 3 }), {
  a: 1,
})

Added in v2.0.0

foldMapWithIndex

Map and fold a Record. Map the Record passing each key/value pair to the iterating function. Then fold the results using the provided Monoid.

Signature

export declare function foldMapWithIndex(
  O: Ord<string>
): <M>(M: Monoid<M>) => <K extends string, A>(f: (k: K, a: A) => M) => (fa: Record<K, A>) => M
export declare function foldMapWithIndex<M>(
  M: Monoid<M>
): <K extends string, A>(f: (k: K, a: A) => M) => (fa: Record<K, A>) => M

Example

import { foldMapWithIndex } from 'fp-ts/Record'
import { Ord } from 'fp-ts/string'
import { Monoid } from 'fp-ts/Monoid'

const m: Monoid<string> = { empty: '', concat: (x: string, y: string) => (x ? `${x} -> ${y}` : `${y}`) }
const f = (k: string, a: number) => `${k}-${a}`
const x = { c: 3, a: 1, b: 2 }
assert.deepStrictEqual(foldMapWithIndex(Ord)(m)(f)(x), 'a-1 -> b-2 -> c-3')

Added in v2.0.0

fromFoldable

Create a Record from a foldable collection of key/value pairs, using the specified Magma to combine values for duplicate keys.

Signature

export declare function fromFoldable<F extends URIS3, A>(
  M: Magma<A>,
  F: Foldable3<F>
): <R, E>(fka: Kind3<F, R, E, [string, A]>) => Record<string, A>
export declare function fromFoldable<F extends URIS2, A>(
  M: Magma<A>,
  F: Foldable2<F>
): <E>(fka: Kind2<F, E, [string, A]>) => Record<string, A>
export declare function fromFoldable<F extends URIS, A>(
  M: Magma<A>,
  F: Foldable1<F>
): (fka: Kind<F, [string, A]>) => Record<string, A>
export declare function fromFoldable<F, A>(
  M: Magma<A>,
  F: FoldableHKT<F>
): (fka: HKT<F, [string, A]>) => Record<string, A>

Added in v2.0.0

fromFoldableMap

Create a Record from a foldable collection using the specified functions to

  • map to key/value pairs
  • combine values for duplicate keys.

Signature

export declare function fromFoldableMap<F extends URIS3, B>(
  M: Magma<B>,
  F: Foldable3<F>
): <R, E, A>(fa: Kind3<F, R, E, A>, f: (a: A) => [string, B]) => Record<string, B>
export declare function fromFoldableMap<F extends URIS2, B>(
  M: Magma<B>,
  F: Foldable2<F>
): <E, A>(fa: Kind2<F, E, A>, f: (a: A) => [string, B]) => Record<string, B>
export declare function fromFoldableMap<F extends URIS, B>(
  M: Magma<B>,
  F: Foldable1<F>
): <A>(fa: Kind<F, A>, f: (a: A) => [string, B]) => Record<string, B>
export declare function fromFoldableMap<F, B>(
  M: Magma<B>,
  F: FoldableHKT<F>
): <A>(fa: HKT<F, A>, f: (a: A) => [string, B]) => Record<string, B>

Example

import { last } from 'fp-ts/Semigroup'
import { Foldable, zip } from 'fp-ts/Array'
import { identity } from 'fp-ts/function'
import { fromFoldableMap } from 'fp-ts/Record'

export const zipObject = <K extends string, A>(keys: Array<K>, values: Array<A>): Record<K, A> =>
  fromFoldableMap(last<A>(), Foldable)(zip(keys, values), identity)

assert.deepStrictEqual(zipObject(['a', 'b'], [1, 2, 3]), { a: 1, b: 2 })

interface User {
  readonly id: string
  readonly name: string
}

const users: Array<User> = [
  { id: 'id1', name: 'name1' },
  { id: 'id2', name: 'name2' },
  { id: 'id1', name: 'name3' },
]

assert.deepStrictEqual(
  fromFoldableMap(last<User>(), Foldable)(users, (user) => [user.id, user]),
  {
    id1: { id: 'id1', name: 'name3' },
    id2: { id: 'id2', name: 'name2' },
  }
)

Added in v2.0.0

has

Test whether or not a key exists in a Record.

Note. This function is not pipeable because is a Refinement.

Signature

export declare const has: <K extends string>(k: string, r: Record<K, unknown>) => k is K

Example

import { has } from 'fp-ts/Record'

assert.deepStrictEqual(has('a', { a: 1, b: 2 }), true)
assert.deepStrictEqual(has('c', { a: 1, b: 2 }), false)

Added in v2.10.0

isEmpty

Test whether a Record is empty.

Signature

export declare const isEmpty: <A>(r: Record<string, A>) => boolean

Example

import { isEmpty } from 'fp-ts/Record'

assert.deepStrictEqual(isEmpty({}), true)
assert.deepStrictEqual(isEmpty({ a: 3 }), false)

Added in v2.0.0

isSubrecord

Test whether one Record contains all of the keys and values contained in another Record.

Signature

export declare const isSubrecord: <A>(
  E: Eq<A>
) => {
  (that: Record<string, A>): (me: Record<string, A>) => boolean
  (me: Record<string, A>, that: Record<string, A>): boolean
}

Example

import { isSubrecord } from 'fp-ts/Record'
import { string } from 'fp-ts'

assert.deepStrictEqual(isSubrecord(string.Eq)({ a: 'foo', b: 'bar', c: 'baz' })({ a: 'foo', b: 'bar', c: 'baz' }), true)
assert.deepStrictEqual(isSubrecord(string.Eq)({ a: 'foo', b: 'bar', c: 'baz' })({ a: 'foo', c: 'baz' }), true)
assert.deepStrictEqual(
  isSubrecord(string.Eq)({ a: 'foo', b: 'bar', c: 'baz' })({ a: 'foo', b: 'not-bar', c: 'baz' }),
  false
)
assert.deepStrictEqual(isSubrecord(string.Eq)({ a: 'foo', b: 'bar' })({ a: 'foo', b: 'bar', c: 'baz' }), false)

Added in v2.0.0

keys

The keys of a Record, sorted alphabetically.

Signature

export declare const keys: <K extends string>(r: Record<K, unknown>) => K[]

Example

import { keys } from 'fp-ts/Record'

assert.deepStrictEqual(keys({ c: 1, a: 2, b: 3 }), ['a', 'b', 'c'])

Added in v2.0.0

lookup

Lookup the value for a key in a Record.

Signature

export declare const lookup: {
  (k: string): <A>(r: Record<string, A>) => Option<A>
  <A>(k: string, r: Record<string, A>): Option<A>
}

Example

import { lookup } from 'fp-ts/Record'
import { option } from 'fp-ts'

assert.deepStrictEqual(lookup('b')({ a: 'foo', b: 'bar' }), option.some('bar'))
assert.deepStrictEqual(lookup('c')({ a: 'foo', b: 'bar' }), option.none)

Added in v2.0.0

map

Map a Record passing the values to the iterating function.

Signature

export declare const map: <A, B>(f: (a: A) => B) => <K extends string>(fa: Record<K, A>) => Record<K, B>

Example

import { map } from 'fp-ts/Record'

const f = (n: number) => `-${n}-`
assert.deepStrictEqual(map(f)({ a: 3, b: 5 }), { a: '-3-', b: '-5-' })

Added in v2.0.0

mapWithIndex

Map a Record passing the key/value pairs to the iterating function.

Signature

export declare const mapWithIndex: <K extends string, A, B>(f: (k: K, a: A) => B) => (fa: Record<K, A>) => Record<K, B>

Example

import { mapWithIndex } from 'fp-ts/Record'

const f = (k: string, n: number) => `${k.toUpperCase()}-${n}`
assert.deepStrictEqual(mapWithIndex(f)({ a: 3, b: 5 }), { a: 'A-3', b: 'B-5' })

Added in v2.0.0

modifyAt

Applies a mapping function to one spcific key/value pair in a Record.

Signature

export declare const modifyAt: <A>(
  k: string,
  f: (a: A) => A
) => <K extends string>(r: Record<K, A>) => Option<Record<K, A>>

Example

import { modifyAt } from 'fp-ts/Record'
import { option } from 'fp-ts'

assert.deepStrictEqual(modifyAt('a', (x: number) => x * 3)({ a: 1, b: 2 }), option.some({ a: 3, b: 2 }))
assert.deepStrictEqual(modifyAt('c', (x: number) => x * 3)({ a: 1, b: 2 }), option.none)

Added in v2.0.0

partitionMapWithIndex

Maps a Record with a function returning an Either and partitions the resulting Record into Lefts and Rights.

Signature

export declare const partitionMapWithIndex: <K extends string, A, B, C>(
  f: (key: K, a: A) => Either<B, C>
) => (fa: Record<K, A>) => Separated<Record<string, B>, Record<string, C>>

Example

import { partitionMapWithIndex } from 'fp-ts/Record'
import { either } from 'fp-ts'

const f = (key: string, a: number) =>
  a >= 0 ? either.right(`${key} is >= 0 (${a})`) : either.left(`${key} is < 0 (${a})`)
assert.deepStrictEqual(partitionMapWithIndex(f)({ a: -1, b: 2, c: 123 }), {
  left: {
    a: 'a is < 0 (-1)',
  },
  right: {
    b: 'b is >= 0 (2)',
    c: 'c is >= 0 (123)',
  },
})

Added in v2.0.0

partitionWithIndex

Partition a Record into two parts according to a predicate that takes a key and a value.

Signature

export declare function partitionWithIndex<K extends string, A, B extends A>(
  refinementWithIndex: RefinementWithIndex<K, A, B>
): (fa: Record<K, A>) => Separated<Record<string, A>, Record<string, B>>
export declare function partitionWithIndex<K extends string, A>(
  predicateWithIndex: PredicateWithIndex<K, A>
): <B extends A>(fb: Record<K, B>) => Separated<Record<string, B>, Record<string, B>>
export declare function partitionWithIndex<K extends string, A>(
  predicateWithIndex: PredicateWithIndex<K, A>
): (fa: Record<K, A>) => Separated<Record<string, A>, Record<string, A>>

Example

import { partitionWithIndex } from 'fp-ts/Record'

assert.deepStrictEqual(
  partitionWithIndex((key: string, a: number) => key.length <= 1 && a > 0)({ a: -1, b: 2, ccc: 7 }),
  {
    left: {
      a: -1,
      ccc: 7,
    },
    right: {
      b: 2,
    },
  }
)

Added in v2.0.0

pop

Delete a key and value from a Record, returning the value as well as the subsequent Record.

Signature

export declare function pop<K extends string>(
  k: K
): <KS extends string, A>(r: Record<KS, A>) => Option<[A, Record<string extends K ? string : Exclude<KS, K>, A>]>

Example

import { pop } from 'fp-ts/Record'
import { option } from 'fp-ts'

assert.deepStrictEqual(pop('a')({ a: 1, b: 2, c: 3 }), option.some([1, { b: 2, c: 3 }]))
assert.deepStrictEqual(pop('x')({ a: 1, b: 2, c: 3 }), option.none)

Added in v2.0.0

reduceRightWithIndex

Same as reduceWithIndex, but reduce starting from the right (i.e. in reverse order, from the last to the first entry according to the given Ord).

Signature

export declare function reduceRightWithIndex(
  O: Ord<string>
): <K extends string, A, B>(b: B, f: (k: K, a: A, b: B) => B) => (fa: Record<K, A>) => B
export declare function reduceRightWithIndex<K extends string, A, B>(
  b: B,
  f: (k: K, a: A, b: B) => B
): (fa: Record<K, A>) => B

Example

import { reduceRightWithIndex } from 'fp-ts/Record'
import { Ord } from 'fp-ts/string'

const x = { c: 3, a: 'foo', b: false }
assert.deepStrictEqual(reduceRightWithIndex(Ord)([] as string[], (k, a, b) => [...b, `${k}-${a}`])(x), [
  'c-3',
  'b-false',
  'a-foo',
])

Added in v2.0.0

reduceWithIndex

Reduces a Record passing each key/value pair to the iterating function. Entries are processed in the order, sorted by key according to the given Ord.

Signature

export declare function reduceWithIndex(
  O: Ord<string>
): <K extends string, A, B>(b: B, f: (k: K, b: B, a: A) => B) => (fa: Record<K, A>) => B
export declare function reduceWithIndex<K extends string, A, B>(
  b: B,
  f: (k: K, b: B, a: A) => B
): (fa: Record<K, A>) => B

Example

import { reduceWithIndex } from 'fp-ts/Record'
import { Ord } from 'fp-ts/string'

const x = { c: 3, a: 'foo', b: false }
assert.deepStrictEqual(reduceWithIndex(Ord)([] as string[], (k, b, a) => [...b, `${k}-${a}`])(x), [
  'a-foo',
  'b-false',
  'c-3',
])

Added in v2.0.0

sequence

Record sequencing, i.e., take a Record in which elements are monads and return a monad of a Record of the base types. The following example for instance shows sequencing a Record<string, Option<number>> into an Option<Record<string, number>>.

sequence in Record is equivalent to sequenceS in Apply.ts.

Signature

export declare function sequence<F extends URIS3>(
  F: Applicative3<F>
): <K extends string, R, E, A>(ta: Record<K, Kind3<F, R, E, A>>) => Kind3<F, R, E, Record<K, A>>
export declare function sequence<F extends URIS3, E>(
  F: Applicative3C<F, E>
): <K extends string, R, A>(ta: Record<K, Kind3<F, R, E, A>>) => Kind3<F, R, E, Record<K, A>>
export declare function sequence<F extends URIS2>(
  F: Applicative2<F>
): <K extends string, E, A>(ta: Record<K, Kind2<F, E, A>>) => Kind2<F, E, Record<K, A>>
export declare function sequence<F extends URIS2, E>(
  F: Applicative2C<F, E>
): <K extends string, A>(ta: Record<K, Kind2<F, E, A>>) => Kind2<F, E, Record<K, A>>
export declare function sequence<F extends URIS>(
  F: Applicative1<F>
): <K extends string, A>(ta: Record<K, Kind<F, A>>) => Kind<F, Record<K, A>>
export declare function sequence<F>(
  F: Applicative<F>
): <K extends string, A>(ta: Record<K, HKT<F, A>>) => HKT<F, Record<K, A>>

Example

import { sequence } from 'fp-ts/Record'
import { option } from 'fp-ts'
import { sequenceS } from 'fp-ts/Apply'

assert.deepStrictEqual(
  sequence(option.Applicative)({ a: option.some(1), b: option.some(2) }),
  option.some({ a: 1, b: 2 })
)
assert.deepStrictEqual(sequence(option.Applicative)({ a: option.some(1), b: option.none }), option.none)
assert.deepStrictEqual(
  sequence(option.Applicative)({ a: option.some(1), b: option.some(2) }),
  sequenceS(option.Applicative)({ a: option.some(1), b: option.some(2) })
)

Added in v2.0.0

singleton

Create a Record with one key/value pair.

Signature

export declare const singleton: <A>(k: string, a: A) => Record<string, A>

Example

import { singleton } from 'fp-ts/Record'

assert.deepStrictEqual(singleton('a', 1), { a: 1 })

Added in v2.0.0

size

Calculate the number of key/value pairs in a Record.

Signature

export declare const size: <A>(r: Record<string, A>) => number

Example

import { size } from 'fp-ts/Record'

assert.deepStrictEqual(size({ a: true, b: 2, c: 'three' }), 3)

Added in v2.0.0

some

Test if at least one value in a Record satisfies the predicate.

Signature

export declare const some: <A>(predicate: (a: A) => boolean) => (r: Record<string, A>) => boolean

Example

import { some } from 'fp-ts/Record'

assert.deepStrictEqual(some((n: number) => n >= 0)({ a: 1, b: -2 }), true)
assert.deepStrictEqual(some((n: number) => n >= 0)({ a: -1, b: -2 }), false)

Added in v2.0.0

toArray

Get a sorted Array of the key/value pairs contained in a Record. Sorted alphabetically by key.

Signature

export declare const toArray: <K extends string, A>(r: Record<K, A>) => [K, A][]

Example

import { toArray } from 'fp-ts/Record'

const x = { c: 3, a: 'foo', b: false }
assert.deepStrictEqual(toArray(x), [
  ['a', 'foo'],
  ['b', false],
  ['c', 3],
])

Added in v2.0.0

toUnfoldable

Unfolds a Record into a list of key/value pairs.

Given an Unfoldable class type U such as array or readonlyArray, it uses the unfold function to create an instance of U, providing an iterating function that iterates over each key/value pair in the record sorted alphabetically by key.

Signature

export declare function toUnfoldable<F extends URIS>(
  U: Unfoldable1<F>
): <K extends string, A>(r: Record<K, A>) => Kind<F, [K, A]>
export declare function toUnfoldable<F>(U: Unfoldable<F>): <K extends string, A>(r: Record<K, A>) => HKT<F, [K, A]>

Example

import { array, readonlyArray } from 'fp-ts'
import { toUnfoldable } from 'fp-ts/Record'

assert.deepStrictEqual(toUnfoldable(array)({ b: 2, a: 1 }), [
  ['a', 1],
  ['b', 2],
])
assert.deepStrictEqual(toUnfoldable(readonlyArray)({ b: 2, a: 1 }), [
  ['a', 1],
  ['b', 2],
])

Added in v2.0.0

traverse

Signature

export declare function traverse<F extends URIS3>(
  F: Applicative3<F>
): <R, E, A, B>(f: (a: A) => Kind3<F, R, E, B>) => <K extends string>(ta: Record<K, A>) => Kind3<F, R, E, Record<K, B>>
export declare function traverse<F extends URIS3, E>(
  F: Applicative3C<F, E>
): <R, A, B>(f: (a: A) => Kind3<F, R, E, B>) => <K extends string>(ta: Record<K, A>) => Kind3<F, R, E, Record<K, B>>
export declare function traverse<F extends URIS2>(
  F: Applicative2<F>
): <E, A, B>(f: (a: A) => Kind2<F, E, B>) => <K extends string>(ta: Record<K, A>) => Kind2<F, E, Record<K, B>>
export declare function traverse<F extends URIS2, E>(
  F: Applicative2C<F, E>
): <A, B>(f: (a: A) => Kind2<F, E, B>) => <K extends string>(ta: Record<K, A>) => Kind2<F, E, Record<K, B>>
export declare function traverse<F extends URIS>(
  F: Applicative1<F>
): <A, B>(f: (a: A) => Kind<F, B>) => <K extends string>(ta: Record<K, A>) => Kind<F, Record<K, B>>
export declare function traverse<F>(
  F: Applicative<F>
): <A, B>(f: (a: A) => HKT<F, B>) => <K extends string>(ta: Record<K, A>) => HKT<F, Record<K, B>>

Added in v2.0.0

traverseWithIndex

Signature

export declare function traverseWithIndex<F extends URIS3>(
  F: Applicative3<F>
): <K extends string, R, E, A, B>(
  f: (k: K, a: A) => Kind3<F, R, E, B>
) => (ta: Record<K, A>) => Kind3<F, R, E, Record<K, B>>
export declare function traverseWithIndex<F extends URIS3, E>(
  F: Applicative3C<F, E>
): <K extends string, R, A, B>(
  f: (k: K, a: A) => Kind3<F, R, E, B>
) => (ta: Record<K, A>) => Kind3<F, R, E, Record<K, B>>
export declare function traverseWithIndex<F extends URIS2>(
  F: Applicative2<F>
): <K extends string, E, A, B>(f: (k: K, a: A) => Kind2<F, E, B>) => (ta: Record<K, A>) => Kind2<F, E, Record<K, B>>
export declare function traverseWithIndex<F extends URIS2, E>(
  F: Applicative2C<F, E>
): <K extends string, A, B>(f: (k: K, a: A) => Kind2<F, E, B>) => (ta: Record<K, A>) => Kind2<F, E, Record<K, B>>
export declare function traverseWithIndex<F extends URIS>(
  F: Applicative1<F>
): <K extends string, A, B>(f: (k: K, a: A) => Kind<F, B>) => (ta: Record<K, A>) => Kind<F, Record<K, B>>
export declare function traverseWithIndex<F>(
  F: Applicative<F>
): <K extends string, A, B>(f: (k: K, a: A) => HKT<F, B>) => (ta: Record<K, A>) => HKT<F, Record<K, B>>

Added in v2.0.0

updateAt

Replace a key/value pair in a Record.

Signature

export declare const updateAt: <A>(k: string, a: A) => <K extends string>(r: Record<K, A>) => Option<Record<K, A>>

Example

import { updateAt } from 'fp-ts/Record'
import { option } from 'fp-ts'

assert.deepStrictEqual(updateAt('a', 3)({ a: 1, b: 2 }), option.some({ a: 3, b: 2 }))
assert.deepStrictEqual(updateAt('c', 3)({ a: 1, b: 2 }), option.none)

Added in v2.0.0

empty

Use a new {} instead.

Signature

export declare const empty: Record<string, never>

Added in v2.0.0

hasOwnProperty (function)

Use has instead.

Signature

export declare const hasOwnProperty: <K extends string>(k: string, r: Record<K, unknown>) => k is K

Added in v2.0.0

insertAt

Use upsertAt instead.

Signature

export declare const insertAt: <A>(k: string, a: A) => (r: Record<string, A>) => Record<string, A>

Added in v2.0.0