CFP - Docs - keepWhen

keepWhen

(predicate: Predicate) => (collection: Collection) => Collection

Keep entries that pass a condition

Try It

const gt2 = n => n > 2
const keepWhenGt2 = keepWhen(gt2)

const result1 = keepWhenGt2([1, 2, 3, 4]) // is [3, 4]
console.log(result1)

const result2 = keepWhenGt2({ a: 1, b: 2, c: 3, d: 4 })
console.log(result2)
// is { c: 3, d: 4 }
const gt2 = (n: number) => n > 2
const keepWhenGt2 = keepWhen(gt2)

const result1 = keepWhenGt2([1, 2, 3, 4]) // is [3, 4]
console.log(result1)

const result2 = keepWhenGt2({ a: 1, b: 2, c: 3, d: 4 })
console.log(result2)
// is { c: 3, d: 4 }

Try It

const gt2 = n => n > 2
const keepWhenGt2 = keepWhen(gt2)

const result1 = keepWhenGt2([1, 2, 3, 4]) // is [3, 4]
console.log(result1)

const result2 = keepWhenGt2({
  a: 1,
  b: 2,
  c: 3,
  d: 4,
})
console.log(result2)
// is { c: 3, d: 4 }
const gt2 = (n: number) => n > 2
const keepWhenGt2 = keepWhen(gt2)

const result1 = keepWhenGt2([1, 2, 3, 4]) // is [3, 4]
console.log(result1)

const result2 = keepWhenGt2({
  a: 1,
  b: 2,
  c: 3,
  d: 4,
})
console.log(result2)
// is { c: 3, d: 4 }

Sometimes we want to keep entries that pass a condition. Below, we have some 100-meter times. People who ran it in under 13 minutes qualify for the next round. Let's list the qualified runners.

Try It

const oneHundredMeterTimes = {
  mary: 12.8,
  sarah: 11.2,
  matt: 13.5,
}

const isSub13m = time => time < 13
const keepSub13Times = keepWhen(isSub13m)

const getQualifiedRunners = compose([keepSub13Times, Object.keys])

const qualified = getQualifiedRunners(oneHundredMeterTimes)
console.log(qualified)
// is [
//   mary
//   sarah
// ]
type Times = Record<string, number>
const oneHundredMeterTimes: Times = {
  mary: 12.8,
  sarah: 11.2,
  matt: 13.5,
}

const isSub13m = (time: number) => time < 13
const keepSub13Times = keepWhen(isSub13m)<Times>

const getQualifiedRunners = compose([keepSub13Times, Object.keys])

const qualifiedRunners = getQualifiedRunners(oneHundredMeterTimes)
console.log(qualifiedRunners)
// is [
//   mary
//   sarah
// ]

Try It

const oneHundredMeterTimes = {
  mary: 12.8,
  sarah: 11.2,
  matt: 13.5,
}

const isSub13m = time => time < 13
const keepSub13Times = keepWhen(isSub13m)

const getQualifiedRunners = compose([
  keepSub13Times,
  Object.keys,
])

const qualified = getQualifiedRunners(
  oneHundredMeterTimes
)
console.log(qualified)
// is [
//   mary
//   sarah
// ]
type Times = Record<string, number>
const oneHundredMeterTimes: Times = {
  mary: 12.8,
  sarah: 11.2,
  matt: 13.5,
}

const isSub13m = (time: number) => time < 13
const keepSub13Times = keepWhen(isSub13m)<Times>

const getQualifiedRunners = compose([
  keepSub13Times,
  Object.keys,
])

const qualifiedRunners = getQualifiedRunners(
  oneHundredMeterTimes
)
console.log(qualifiedRunners)
// is [
//   mary
//   sarah
// ]