CFP - Docs - mDiscardLastWhile

mDiscardLastWhile

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

Discard the last elements that pass a condition

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

Try It

const gt2 = n => n > 2
const mDiscardLastWhileGt2 = mDiscardLastWhile(gt2)

const arr = [1, 2, 3, 4]
const mutatedArr = mDiscardLastWhileGt2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]
const gt2 = (n: number) => n > 2
const mDiscardLastWhileGt2 = mDiscardLastWhile(gt2)

const arr = [1, 2, 3, 4]
const mutatedArr = mDiscardLastWhileGt2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]

Try It

const gt2 = n => n > 2
const mDiscardLastWhileGt2 =
  mDiscardLastWhile(gt2)

const arr = [1, 2, 3, 4]
const mutatedArr = mDiscardLastWhileGt2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]
const gt2 = (n: number) => n > 2
const mDiscardLastWhileGt2 =
  mDiscardLastWhile(gt2)

const arr = [1, 2, 3, 4]
const mutatedArr = mDiscardLastWhileGt2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]

This is useful when we have sorted data and don't need to filter over all of it. Below, we have a list of accounts ordered by activity. Let's remove accounts that have been inactive for at least a year.

Try It

const accounts = [
  { id: 'ken@example.com', lastActive: '2024 2 16' },
  { id: 'chris@example.com', lastActive: '2024 2 15' },
  { id: 'liz@example.com', lastActive: '2024 2 15' },
]

const yearAgo = new Date('2024 2 15')
const isInactiveForAYear = ({ lastActive }) => {
  const lastActiveDate = new Date(lastActive)
  return lastActiveDate <= yearAgo
}
const discardInactiveAccounts = mDiscardLastWhile(isInactiveForAYear)
discardInactiveAccounts(accounts)
console.log(accounts)
// is [{
//   id: ken@example.com
//   lastActive: 2024 2 16
// }]
type Account = {
  id: string
  lastActive: string
}

const accounts: Account[] = [
  { id: 'ken@example.com', lastActive: '2024 2 16' },
  { id: 'chris@example.com', lastActive: '2024 2 15' },
  { id: 'liz@example.com', lastActive: '2024 2 15' },
]

const yearAgo = new Date('2024 2 15')
const beenInactiveForAYear = ({ lastActive }: Account) => {
  const lastActiveDate = new Date(lastActive)
  return lastActiveDate <= yearAgo
}
const discardInactiveAccounts = mDiscardLastWhile(beenInactiveForAYear)
discardInactiveAccounts(accounts)
console.log(accounts)
// is [{
//   id: ken@example.com
//   lastActive: 2024 2 16
// }]

Try It

const accounts = [
  {
    id: 'ken@example.com',
    lastActive: '2024 2 16',
  },
  {
    id: 'chris@example.com',
    lastActive: '2024 2 15',
  },
  {
    id: 'liz@example.com',
    lastActive: '2024 2 15',
  },
]

const yearAgo = new Date('2024 2 15')
const isInactiveForAYear = ({ lastActive }) => {
  const lastActiveDate = new Date(lastActive)
  return lastActiveDate <= yearAgo
}
const discardInactiveAccounts = mDiscardLastWhile(
  isInactiveForAYear
)
discardInactiveAccounts(accounts)
console.log(accounts)
// is [{
//   id: ken@example.com
//   lastActive: 2024 2 16
// }]
type Account = {
  id: string
  lastActive: string
}

const accounts: Account[] = [
  {
    id: 'ken@example.com',
    lastActive: '2024 2 16',
  },
  {
    id: 'chris@example.com',
    lastActive: '2024 2 15',
  },
  {
    id: 'liz@example.com',
    lastActive: '2024 2 15',
  },
]

const yearAgo = new Date('2024 2 15')
const beenInactiveForAYear = ({
  lastActive,
}: Account) => {
  const lastActiveDate = new Date(lastActive)
  return lastActiveDate <= yearAgo
}
const discardInactiveAccounts = mDiscardLastWhile(
  beenInactiveForAYear
)
discardInactiveAccounts(accounts)
console.log(accounts)
// is [{
//   id: ken@example.com
//   lastActive: 2024 2 16
// }]