CFP - Docs - keepLastWhile

keepLastWhile

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

Keep the last elements that pass a condition

Try It

const keepLastWhileGt1 = keepLastWhile(n => n > 1)

keepLastWhileGt1([1, 2, 3]) // is [2, 3]
keepLastWhileGt1([2, 3, 1]) // is []
const keepLastWhileGt1 = keepLastWhile((n: number) => n > 1)

keepLastWhileGt1([1, 2, 3]) // is [2, 3]
keepLastWhileGt1([2, 3, 1]) // is []

Try It

const keepLastWhileGt1 = keepLastWhile(n => n > 1)

keepLastWhileGt1([1, 2, 3]) // is [2, 3]
keepLastWhileGt1([2, 3, 1]) // is []
const keepLastWhileGt1 = keepLastWhile(
  (n: number) => n > 1
)

keepLastWhileGt1([1, 2, 3]) // is [2, 3]
keepLastWhileGt1([2, 3, 1]) // is []

Sometimes we have ordered data and only care about the last elements. Below, we are running a streaming service and have added a few new cooking shows. We only renew shows with at least a thousand views, so let's list the ones we need to cancel.

Try It

const shows = [
  { name: "Cake'n'Bake", views: 2047 },
  { name: "Greg's Grills", views: 688 },
  { name: "Let's Brunch", views: 512 },
]

const shouldCancel = ({ views }) => views < 1000

const getCanceledShows = compose([
  keepLastWhile(shouldCancel),
  mapValues(get('name')),
])

const canceledShows = getCanceledShows(shows)
console.log(canceledShows)
// is [
//   Greg's Grills
//   Let's Brunch
// ]
type Show = {
  name: string
  views: number
}

const shows: Show[] = [
  { name: "Cake'n'Bake", views: 2047 },
  { name: "Greg's Grills", views: 688 },
  { name: "Let's Brunch", views: 512 },
]

const shouldCancel = ({ views }: Show) => views < 1000
const getName = get('name')<Show>

const getCanceledShows = compose([
  keepLastWhile(shouldCancel)<Show[]>,
  mapValues(getName)<Show[]>,
])

const canceledShows = getCanceledShows(shows)
console.log(canceledShows)
// is [
//   Greg's Grills
//   Let's Brunch
// ]

Try It

const shows = [
  { name: "Cake'n'Bake", views: 2047 },
  { name: "Greg's Grills", views: 688 },
  { name: "Let's Brunch", views: 512 },
]

const shouldCancel = ({ views }) => views < 1000

const getCanceledShows = compose([
  keepLastWhile(shouldCancel),
  mapValues(get('name')),
])

const canceledShows = getCanceledShows(shows)
console.log(canceledShows)
// is [
//   Greg's Grills
//   Let's Brunch
// ]
type Show = {
  name: string
  views: number
}

const shows: Show[] = [
  { name: "Cake'n'Bake", views: 2047 },
  { name: "Greg's Grills", views: 688 },
  { name: "Let's Brunch", views: 512 },
]

const shouldCancel = ({ views }: Show) =>
  views < 1000
const getName = get('name')<Show>

const getCanceledShows = compose([
  keepLastWhile(shouldCancel)<Show[]>,
  mapValues(getName)<Show[]>,
])

const canceledShows = getCanceledShows(shows)
console.log(canceledShows)
// is [
//   Greg's Grills
//   Let's Brunch
// ]