map transforms, filter keeps, reduce folds to one value.

Goal

Sum shillings for busy kiosks.

const units = [12, 8, 5];
console.log(units.map((n) => n * 40));

const rows = [
  { city: "Nairobi", units: 12 },
  { city: "Mombasa", units: 8 },
  { city: "Kisumu", units: 5 },
];
console.log(rows.filter((r) => r.units >= 8).map((r) => r.city));

const units = [12, 8, 5];
const sum = units.reduce((acc, n) => acc + n, 0);
console.log(sum);

const rows = [
  { city: "Nairobi", shillings: 480 },
  { city: "Nakuru", shillings: 160 },
];
console.log(rows.reduce((acc, r) => acc + r.shillings, 0));