CFP - Docs - keepFirst

keepFirst

(num: number) => (sequence: Sequence) => Sequence

Keep the first num elements of a sequence

Try It

const keepFirstThree = keepFirst(3)

keepFirstThree(['a', 'b', 'c', 'd']) // is ['a', 'b', 'c']
keepFirstThree('abcd') // is 'abc'
keepFirstThree(['a']) // is ['a']
const keepFirstThree = keepFirst(3)

keepFirstThree(['a', 'b', 'c', 'd']) // is ['a', 'b', 'c']
keepFirstThree('abcd') // is 'abc'
keepFirstThree(['a']) // is ['a']

Try It

const keepFirstThree = keepFirst(3)

keepFirstThree(['a', 'b', 'c', 'd']) // is ['a', 'b', 'c']
keepFirstThree('abcd') // is 'abc'
keepFirstThree(['a']) // is ['a']
const keepFirstThree = keepFirst(3)

keepFirstThree(['a', 'b', 'c', 'd']) // is ['a', 'b', 'c']
keepFirstThree('abcd') // is 'abc'
keepFirstThree(['a']) // is ['a']

Sometimes we have ordered data and only care about the first elements. Below, we have a list of boots ordered by number sold. Let's display our top three selling boots.

Try It

const bootsByNumSold = [
  {
    name: 'Columbia Escape',
    sold: 82,
  },
  {
    name: 'Keen Gibson',
    sold: 79,
  },
  {
    name: 'Timberland Classic',
    sold: 65,
  },
  {
    name: 'Nortiv Armadillo',
    sold: 58,
  },
]

const keepTopThree = keepFirst(3)
const getTopSellers = compose([
  keepTopThree,
  mapValues(get('name')),
  joinValues(', '),
])
const topSellers = getTopSellers(bootsByNumSold)
console.log(topSellers)
// prints
// Columbia Escape, Keen Gibson, Timberland Classic
type Boot = {
  name: string
  sold: number
}

const bootsByNumSold = [
  {
    name: 'Columbia Escape',
    sold: 82,
  },
  {
    name: 'Keen Gibson',
    sold: 79,
  },
  {
    name: 'Timberland Classic',
    sold: 65,
  },
  {
    name: 'Nortiv Armadillo',
    sold: 58,
  },
]

const keepTopThree = keepFirst(3)<Boot[]>
const getTopSellers = compose([
  keepTopThree,
  mapValues(get('name')),
  joinValues(', '),
])
const topSellers = getTopSellers(bootsByNumSold)
console.log(topSellers)
// prints
// Columbia Escape, Keen Gibson, Timberland Classic

Try It

const bootsByNumSold = [
  {
    name: 'Columbia Escape',
    sold: 82,
  },
  {
    name: 'Keen Gibson',
    sold: 79,
  },
  {
    name: 'Timberland Classic',
    sold: 65,
  },
  {
    name: 'Nortiv Armadillo',
    sold: 58,
  },
]

const keepTopThree = keepFirst(3)
const getTopSellers = compose([
  keepTopThree,
  mapValues(get('name')),
  joinValues(', '),
])
const topSellers = getTopSellers(bootsByNumSold)
console.log(topSellers)
// prints
// Columbia Escape, Keen Gibson, Timberland Classic
type Boot = {
  name: string
  sold: number
}

const bootsByNumSold = [
  {
    name: 'Columbia Escape',
    sold: 82,
  },
  {
    name: 'Keen Gibson',
    sold: 79,
  },
  {
    name: 'Timberland Classic',
    sold: 65,
  },
  {
    name: 'Nortiv Armadillo',
    sold: 58,
  },
]

const keepTopThree = keepFirst(3)<Boot[]>
const getTopSellers = compose([
  keepTopThree,
  mapValues(get('name')),
  joinValues(', '),
])
const topSellers = getTopSellers(bootsByNumSold)
console.log(topSellers)
// prints
// Columbia Escape, Keen Gibson, Timberland Classic