CFP - Docs - mKeepFirstWhile

mKeepFirstWhile

(predicate: Predicate) => (anArray: array) => anArray

Keep the first elements of an array that pass a condition

Consider keepFirstWhile instead.
This is for the uncommon case where mutating anArray is required.

Try It

const lt3 = n => n < 3
const mKeepFirstWhileLt3 = mKeepFirstWhile(lt3)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepFirstWhileLt3(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]
const lt3 = (n: number) => n < 3
const mKeepFirstWhileLt3 = mKeepFirstWhile(lt3)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepFirstWhileLt3(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]

Try It

const lt3 = n => n < 3
const mKeepFirstWhileLt3 = mKeepFirstWhile(lt3)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepFirstWhileLt3(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]
const lt3 = (n: number) => n < 3
const mKeepFirstWhileLt3 = mKeepFirstWhile(lt3)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepFirstWhileLt3(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]

Sometimes we have ordered data and only care about the first elements. Below, we have students who sold magazine subscriptions, ordered by number sold. Students who sold ten or more get to ride a limo over lunch. Let's see who rides the limo.

Try It

const sellers = [
  { name: 'phil', numSold: 15 },
  { name: 'mary', numSold: 11 },
  { name: 'sarah', numSold: 8 },
]

const soldAtLeast10 = ({ numSold }) => numSold >= 10
const keepRewardRecipients = mKeepFirstWhile(soldAtLeast10)
keepRewardRecipients(sellers)
const getNames = mapValues(get('name'))
const rewardRecipients = getNames(sellers)
console.log(rewardRecipients)
// is [
//   phil
//   mary
// ]
type Seller = {
  name: string
  numSold: number
}
const sellers: Seller[] = [
  { name: 'phil', numSold: 15 },
  { name: 'mary', numSold: 11 },
  { name: 'sarah', numSold: 8 },
]

const soldAtLeast10 = ({ numSold }: Seller) => numSold >= 10
const keepRewardRecipients = mKeepFirstWhile(soldAtLeast10)
keepRewardRecipients(sellers)
const getName = get('name')<Seller>
const getAllNames = mapValues(getName)<Seller[]>
const rewardRecipients = getAllNames(sellers)
console.log(rewardRecipients)
// is [
//   phil
//   mary
// ]

Try It

const sellers = [
  { name: 'phil', numSold: 15 },
  { name: 'mary', numSold: 11 },
  { name: 'sarah', numSold: 8 },
]

const soldAtLeast10 = ({ numSold }) =>
  numSold >= 10
const keepRewardRecipients = mKeepFirstWhile(
  soldAtLeast10
)
keepRewardRecipients(sellers)
const getNames = mapValues(get('name'))
const rewardRecipients = getNames(sellers)
console.log(rewardRecipients)
// is [
//   phil
//   mary
// ]
type Seller = {
  name: string
  numSold: number
}
const sellers: Seller[] = [
  { name: 'phil', numSold: 15 },
  { name: 'mary', numSold: 11 },
  { name: 'sarah', numSold: 8 },
]

const soldAtLeast10 = ({ numSold }: Seller) =>
  numSold >= 10
const keepRewardRecipients = mKeepFirstWhile(
  soldAtLeast10
)
keepRewardRecipients(sellers)
const getName = get('name')<Seller>
const getAllNames = mapValues(getName)<Seller[]>
const rewardRecipients = getAllNames(sellers)
console.log(rewardRecipients)
// is [
//   phil
//   mary
// ]