CFP - Docs - mDiscardLast

mDiscardLast

(num: number) => (anArray: array) => anArray

Discard the last num values

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

Try It

const mDiscardLast2 = mDiscardLast(2)
const arr = [1, 2, 3, 4]
const mutatedArr = mDiscardLast2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]
const mDiscardLast2 = mDiscardLast(2)
const arr = [1, 2, 3, 4]
const mutatedArr = mDiscardLast2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]

Try It

const mDiscardLast2 = mDiscardLast(2)
const arr = [1, 2, 3, 4]
const mutatedArr = mDiscardLast2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]
const mDiscardLast2 = mDiscardLast(2)
const arr = [1, 2, 3, 4]
const mutatedArr = mDiscardLast2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [1, 2]

Sometimes we get data in the form of arrays rather than objects. Below, we have weather data from a spreadsheet. For now we don't care about the max wind speed nor climate columns, so let's remove them.

Try It

const [_headers, ...weatherData] = [
  ['date', 'low', 'high', 'wind', 'climate'],
  ['2025-04-08', 35, 50, 15, 'sunny'],
  ['2025-04-09', 40, 55, 10, 'cloudy'],
  ['2025-04-10', 38, 52, 12, 'rain shower'],
]

const discardWindAndClimate = mDiscardLast(2)
const discardAllWindAndClimate = forEach(discardWindAndClimate)
discardAllWindAndClimate(weatherData)
console.log(weatherData)
// is [
//  ['2025-04-08', 35, 50],
//  ['2025-04-09', 40, 55],
//  ['2025-04-10', 38, 52],
// ]
type Row = Array<string | number>
type WeatherData = Row[]
const [_headers, ...weatherData]: [string[], ...WeatherData] = [
  ['date', 'low', 'high', 'wind', 'climate'],
  ['2025-04-08', 35, 50, 15, 'sunny'],
  ['2025-04-09', 40, 55, 10, 'cloudy'],
  ['2025-04-10', 38, 52, 12, 'rain shower'],
]

const discardWindAndClimate = mDiscardLast(2)<Row>
const discardAllWindAndClimate = forEach(discardWindAndClimate)<WeatherData>
discardAllWindAndClimate(weatherData)
console.log(weatherData)
// is [
//  ['2025-04-08', 35, 50],
//  ['2025-04-09', 40, 55],
//  ['2025-04-10', 38, 52],
// ]

Try It

const [_headers, ...weatherData] = [
  ['date', 'low', 'high', 'wind', 'climate'],
  ['2025-04-08', 35, 50, 15, 'sunny'],
  ['2025-04-09', 40, 55, 10, 'cloudy'],
  ['2025-04-10', 38, 52, 12, 'rain shower'],
]

const discardWindAndClimate = mDiscardLast(2)
const discardAllWindAndClimate = forEach(
  discardWindAndClimate
)
discardAllWindAndClimate(weatherData)
console.log(weatherData)
// is [
//  ['2025-04-08', 35, 50],
//  ['2025-04-09', 40, 55],
//  ['2025-04-10', 38, 52],
// ]
type Row = Array<string | number>
type WeatherData = Row[]
const [_headers, ...weatherData]: [
  string[],
  ...WeatherData,
] = [
  ['date', 'low', 'high', 'wind', 'climate'],
  ['2025-04-08', 35, 50, 15, 'sunny'],
  ['2025-04-09', 40, 55, 10, 'cloudy'],
  ['2025-04-10', 38, 52, 12, 'rain shower'],
]

const discardWindAndClimate = mDiscardLast(2)<Row>
const discardAllWindAndClimate = forEach(
  discardWindAndClimate
)<WeatherData>
discardAllWindAndClimate(weatherData)
console.log(weatherData)
// is [
//  ['2025-04-08', 35, 50],
//  ['2025-04-09', 40, 55],
//  ['2025-04-10', 38, 52],
// ]