CFP - Docs - invert

invert

(collection: KeyedCollection) => KeyedCollection

Swap the values and keys of a KeyedCollection

Try It

invert({ a: 1, b: 2 }) // is { 1: 'a', 2: 'b' }

const aMap = new Map([
  ['a', 1],
  ['b', 2],
])
invert(aMap) // is a new Map [[1, 'a'], [2, 'b']]
invert({ a: 1, b: 2 }) // is { 1: 'a', 2: 'b' }

const aMap = new Map([
  ['a', 1],
  ['b', 2],
])
invert(aMap) // is a new Map [[1, 'a'], [2, 'b']]

Try It

invert({ a: 1, b: 2 }) // is { 1: 'a', 2: 'b' }

const aMap = new Map([
  ['a', 1],
  ['b', 2],
])
invert(aMap) // is a new Map [[1, 'a'], [2, 'b']]
invert({ a: 1, b: 2 }) // is { 1: 'a', 2: 'b' }

const aMap = new Map([
  ['a', 1],
  ['b', 2],
])
invert(aMap) // is a new Map [[1, 'a'], [2, 'b']]

One common case for invert is to get a two-way enum mapping. Below, we run a stock reporting website. People don't remember stock symbols, so we can use invert to convert between symbols and company names. With that, let's create a report for our users, as well as let them query the price for a single company.

Try It

const companyByStock = {
  NVDA: 'NVIDIA',
  AAPL: 'Apple',
}
const stockByCompany = invert(companyByStock)
const stockPrices = {
  AAPL: 200,
  NVDA: 150,
}

const formatPrice = (price, stock) => {
  const company = companyByStock[stock]
  return `  ${company} - $${price}`
}
const formatAllPrices = mapValues(formatPrice)
const createReport = compose([
  formatAllPrices,
  joinValues('\n'),
  prepend('Company Stock Prices\n'),
])
const report = createReport(stockPrices)
console.log(report)
// is
// Company Stock Prices
//   Apple - $200
//   Nvidia - $150

const getPriceForCompany = company => {
  const stock = stockByCompany[company]
  return stockPrices[stock]
}

const price = getPriceForCompany('Apple')
console.log(price) // is 200
type Stock = 'NVDA' | 'AAPL'
type Company = 'NVIDIA' | 'Apple'

const companyByStock = {
  NVDA: 'NVIDIA',
  AAPL: 'Apple',
} as const
const stockByCompany = invert(companyByStock)
const stockPrices: Record<Stock, number> = {
  AAPL: 200,
  NVDA: 150,
}

const formatPrice = (price: number, stock: Stock) => {
  const company = companyByStock[stock]
  return `  ${company} - $${price}`
}
const formatAllPrices = mapValues(formatPrice)<Record<Stock, number>>
const createReport = compose([
  formatAllPrices,
  joinValues('\n'),
  prepend('Company Stock Prices\n'),
])
const report = createReport(stockPrices)
console.log(report)
// is
// Company Stock Prices
//   Apple - $200
//   Nvidia - $150

const getPriceForCompany = (company: Company) => {
  const stock = stockByCompany[company]
  return stockPrices[stock]
}

const price = getPriceForCompany('Apple')
console.log(price) // is 200

Try It

const companyByStock = {
  NVDA: 'NVIDIA',
  AAPL: 'Apple',
}
const stockByCompany = invert(companyByStock)
const stockPrices = {
  AAPL: 200,
  NVDA: 150,
}

const formatPrice = (price, stock) => {
  const company = companyByStock[stock]
  return `  ${company} - $${price}`
}
const formatAllPrices = mapValues(formatPrice)
const createReport = compose([
  formatAllPrices,
  joinValues('\n'),
  prepend('Company Stock Prices\n'),
])
const report = createReport(stockPrices)
console.log(report)
// is
// Company Stock Prices
//   Apple - $200
//   Nvidia - $150

const getPriceForCompany = company => {
  const stock = stockByCompany[company]
  return stockPrices[stock]
}

const price = getPriceForCompany('Apple')
console.log(price) // is 200
type Stock = 'NVDA' | 'AAPL'
type Company = 'NVIDIA' | 'Apple'

const companyByStock = {
  NVDA: 'NVIDIA',
  AAPL: 'Apple',
} as const
const stockByCompany = invert(companyByStock)
const stockPrices: Record<Stock, number> = {
  AAPL: 200,
  NVDA: 150,
}

const formatPrice = (
  price: number,
  stock: Stock
) => {
  const company = companyByStock[stock]
  return `  ${company} - $${price}`
}
const formatAllPrices = mapValues(formatPrice)<
  Record<Stock, number>
>
const createReport = compose([
  formatAllPrices,
  joinValues('\n'),
  prepend('Company Stock Prices\n'),
])
const report = createReport(stockPrices)
console.log(report)
// is
// Company Stock Prices
//   Apple - $200
//   Nvidia - $150

const getPriceForCompany = (company: Company) => {
  const stock = stockByCompany[company]
  return stockPrices[stock]
}

const price = getPriceForCompany('Apple')
console.log(price) // is 200