CFP - Docs - mKeepLast

mKeepLast

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

Keep the last num elements of an array

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

Try It

const mKeepLast2 = mKeepLast(2)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepLast2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [3, 4]
const mKeepLast2 = mKeepLast(2)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepLast2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [3, 4]

Try It

const mKeepLast2 = mKeepLast(2)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepLast2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [3, 4]
const mKeepLast2 = mKeepLast(2)

const arr = [1, 2, 3, 4]
const mutatedArr = mKeepLast2(arr)
console.log(mutatedArr === arr) // is true
console.log(arr) // is [3, 4]

Sometimes we have ordered data and only care about the last items. Below, we run a shop "Brooke's Books" and are preparing for our monthly meeting. Let's report our sales for the last two months.

Try It

const salesByMonth = [
  ['month', 'subscriptions', 'books'],
  ['Jan', 129, 561],
  ['Feb', 98, 523],
  ['Mar', 112, 530],
  ['Apr', 107, 588],
]

const keepMostRecent2Months = mKeepLast(2)
keepMostRecent2Months(salesByMonth)

const format = sales => {
  const [month, subsSold, booksSold] = sales
  return [
    month,
    `  subscriptions: ${subsSold}`,
    `  books:         ${booksSold}`,
  ].join('\n')
}

const createReport = compose([
  mapValues(format),
  prependOne('Sales From Last Two Months'),
  joinValues('\n'),
])
const report = createReport(salesByMonth)

console.log(report)
// prints
// Sales From Last Two Months
// Mar
//   subscriptions: 112
//   books:         530
// Apr
//   subscriptions: 107
//   books:         588
type Row = Array<string | number>

const salesByMonth: Row[] = [
  ['month', 'subscriptions', 'books'],
  ['Jan', 129, 561],
  ['Feb', 98, 523],
  ['Mar', 112, 530],
  ['Apr', 107, 588],
]

const keepMostRecent2Months = mKeepLast(2)<Row[]>
keepMostRecent2Months(salesByMonth)

const format = (sales: Row) => {
  const [month, subsSold, booksSold] = sales
  return [
    month,
    `  subscriptions: ${subsSold}`,
    `  books:         ${booksSold}`,
  ].join('\n')
}

const createReport = compose([
  mapValues(format)<Row[]>,
  prependOne('Sales From Last Two Months'),
  joinValues('\n'),
])
const report = createReport(salesByMonth)

console.log(report)
// prints
// Sales From Last Two Months
// Mar
//   subscriptions: 112
//   books:         530
// Apr
//   subscriptions: 107
//   books:         588

Try It

const salesByMonth = [
  ['month', 'subscriptions', 'books'],
  ['Jan', 129, 561],
  ['Feb', 98, 523],
  ['Mar', 112, 530],
  ['Apr', 107, 588],
]

const keepMostRecent2Months = mKeepLast(2)
keepMostRecent2Months(salesByMonth)

const format = sales => {
  const [month, subsSold, booksSold] = sales
  return [
    month,
    `  subscriptions: ${subsSold}`,
    `  books:         ${booksSold}`,
  ].join('\n')
}

const createReport = compose([
  mapValues(format),
  prependOne('Sales From Last Two Months'),
  joinValues('\n'),
])
const report = createReport(salesByMonth)

console.log(report)
// prints
// Sales From Last Two Months
// Mar
//   subscriptions: 112
//   books:         530
// Apr
//   subscriptions: 107
//   books:         588
type Row = Array<string | number>

const salesByMonth: Row[] = [
  ['month', 'subscriptions', 'books'],
  ['Jan', 129, 561],
  ['Feb', 98, 523],
  ['Mar', 112, 530],
  ['Apr', 107, 588],
]

const keepMostRecent2Months = mKeepLast(2)<Row[]>
keepMostRecent2Months(salesByMonth)

const format = (sales: Row) => {
  const [month, subsSold, booksSold] = sales
  return [
    month,
    `  subscriptions: ${subsSold}`,
    `  books:         ${booksSold}`,
  ].join('\n')
}

const createReport = compose([
  mapValues(format)<Row[]>,
  prependOne('Sales From Last Two Months'),
  joinValues('\n'),
])
const report = createReport(salesByMonth)

console.log(report)
// prints
// Sales From Last Two Months
// Mar
//   subscriptions: 112
//   books:         530
// Apr
//   subscriptions: 107
//   books:         588