ReadonlyRecord overview

This module targets readonly objects in the sense of maps. For readonly objects in the sense of product types see the ReadonlyStruct module.

Added in v0.10.0

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Table of contents

• 3 Functions
  • invertAll
  • invertLast
  • lookupV
  • omit
  • pick
  • reject
  • values

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3 Functions

invertAll

Invert a record, collecting values with duplicate keys in an array. Should you only care about the last item or are not worried about the risk of duplicate keys, see instead invertLast.

Signature

export declare const invertAll: <A>(
  f: (x: A) => string
) => (x: Readonly<Record<string, A>>) => RR.ReadonlyRecord<string, ReadonlyArray<string>>

Example

import { invertAll } from 'fp-ts-std/ReadonlyRecord'
import { fromNumber } from 'fp-ts-std/String'

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

Added in v0.10.0

invertLast

Invert a record, keeping only the last value should the same key be encountered more than once. If you’d like to keep the values that would be lost, see instead invertAll.

Signature

export declare const invertLast: <A>(
  f: (x: A) => string
) => (x: Readonly<Record<string, A>>) => RR.ReadonlyRecord<string, string>

Example

import { invertLast } from 'fp-ts-std/ReadonlyRecord'
import { fromNumber } from 'fp-ts-std/String'

assert.deepStrictEqual(invertLast(fromNumber)({ a: 1, b: 2, c: 2, d: 3 }), { '1': 'a', '2': 'c', '3': 'd' })

Added in v0.10.0

lookupV

Like fp-ts/ReadonlyRecord::lookup but flipped, which the “V” suffix denotes.

Signature

export declare const lookupV: <A>(x: Readonly<Record<string, A>>) => (k: string) => Option<A>

lookupV :: Readonly (Record string a) -> string -> Option a

Example

import { lookupV } from 'fp-ts-std/ReadonlyRecord'
import * as A from 'fp-ts/Array'

const x = { a: 1, b: 'two', c: [true] }
const ks = ['a', 'c']

assert.deepStrictEqual(A.filterMap(lookupV(x))(ks), [1, [true]])

Added in v0.10.0

omit

Omit a set of keys from a ReadonlyRecord. The value-level equivalent of the Omit type. For omitting from records with typed keys, instead look at the ReadonlyStruct module.

Signature

export declare const omit: (ks: Array<string>) => <A>(y: Record<string, A>) => Record<string, A>

omit :: Array string -> Record string a -> Record string a

Example

import { omit } from 'fp-ts-std/ReadonlyRecord'
import { pipe } from 'fp-ts/function'

const remaining = pipe({ a: 1, b: 'two', c: [true] }, omit(['b']))

assert.deepStrictEqual(remaining, { a: 1, c: [true] })

Added in v0.16.0

pick

Pick a set of keys from a ReadonlyRecord. The value-level equivalent of the Pick type. For picking records with typed keys, instead look at the ReadonlyStruct module.

Signature

export declare const pick: (
  ks: ReadonlyArray<string>
) => <A>(y: Readonly<Record<string, A>>) => Readonly<Record<string, A>>

pick :: ReadonlyArray string -> Readonly (Record string a) -> Readonly (Record string a)

Example

import { pick } from 'fp-ts-std/ReadonlyRecord'
import { pipe } from 'fp-ts/function'

const picked = pipe({ a: 1, b: 'two', c: [true] }, pick(['a', 'c']))

assert.deepStrictEqual(picked, { a: 1, c: [true] })

Added in v0.16.0

reject

Filters out key/value pairs in the record for which the predicate upon the value holds. This can be thought of as the inverse of ordinary record filtering.

Signature

export declare const reject: <A>(
  f: Predicate<A>
) => <B extends A>(x: Readonly<Record<string, B>>) => Readonly<Record<string, B>>

reject :: b extends a => Predicate a -> Readonly (Record string b) -> Readonly (Record string b)

Example

import { reject } from 'fp-ts-std/ReadonlyRecord'
import { Predicate } from 'fp-ts/Predicate'

const isEven: Predicate<number> = (n) => n % 2 === 0

assert.deepStrictEqual(reject(isEven)({ a: 1, b: 2, c: 3, d: 4 }), { a: 1, c: 3 })

Added in v0.10.0

values

Get the values from a Record.

Signature

export declare const values: <A>(x: Readonly<Record<string, A>>) => readonly A[]

values :: Readonly (Record string a) -> Array a

Example

import { values } from 'fp-ts-std/ReadonlyRecord'

const x = { a: 1, b: 'two' }

assert.deepStrictEqual(values(x), [1, 'two'])

Added in v0.10.0