map and multi-dim arrays

map.js

// Data

const account1 = {
  owner: 'Bobby Khan',
  movements: [2030, 450, -400, 3000, -650, -130, 70, 1300],
  interestRate: 1.2, // %
  pin: 11411,
};

const account2 = {
  owner: 'Trevor Hanson',
  movements: [50200, 3400, -150, -790, -3210, -1000, 8500, -30],
  interestRate: 1.5,
  pin: 2222,
};

const account3 = {
  owner: 'Grace Kelly',
  movements: [2200, -200, 340, -300, -20, 50, 400, -460],
  interestRate: 0.7,
  pin: 3333,
};

const account4 = {
  owner: 'Rusty Shackleford',
  movements: [4430, 1000, 700, 50, 90],
  interestRate: 1,
  pin: 4444,
};

const accounts = [account1, account2, account3, account4];

// output
// access accounts array
// flaten array
// get sum

const overallBalance = accounts
.map(acc => acc.movements)
.flat()
.reduce((acc, mov) => acc + mov, 0);

// 17840
console.log(overallBalance);

// flatMap (better performance)

const overallBalance2 = accounts
  .flatMap(acc => acc.movements)
  .reduce((acc, mov) => acc + mov, 0);

// same result 17840
console.log(overallBalance2);