[Compose] Compose exercises

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// Setup
//==============
const _ = R;
const {formatMoney} = accounting;
 
// Example Data
const CARS = [
    {name: "Ferrari FF", horsepower: 660, dollar_value: 700000, in_stock: true},
    {name: "Spyker C12 Zagato", horsepower: 650, dollar_value: 648000, in_stock: false},
    {name: "Jaguar XKR-S", horsepower: 550, dollar_value: 132000, in_stock: false},
    {name: "Audi R8", horsepower: 525, dollar_value: 114200, in_stock: false},
    {name: "Aston Martin One-77", horsepower: 750, dollar_value: 1850000, in_stock: true},
    {name: "Pagani Huayra", horsepower: 700, dollar_value: 1300000, in_stock: false}
  ];
 
// Exercise 1:
// ============
// use _.compose() to rewrite the function below. Hint: _.prop() is curried.
 
const isLastInStock = _.compose(
  _.prop('in_stock'),
  _.last
)
 
QUnit.test("Ex1: isLastInStock", assert => {
  assert.deepEqual(isLastInStock(CARS), false);
})
 
''
 
 
// Exercise 2:
// ============
// use _.compose(), _.prop() and _.head() to retrieve the name of the first car
 
const nameOfFirstCar = _.compose(
  _.prop('name'),
  _.head
)
 
QUnit.test("Ex2: nameOfFirstCar", assert => {
  assert.equal(nameOfFirstCar(CARS), "Ferrari FF");
})
 
// Exercise 3:
// ============
// Use the helper function _average to refactor averageDollarValue as a composition
 
const _average = function(xs) { return _.reduce(_.add, 0, xs) / xs.length; }; // <- leave be
 
const averageDollarValue = _.compose(
  _average,
  _.map(_.prop('dollar_value'))
)
 
QUnit.test("Ex3: averageDollarValue", assert => {
  assert.equal(averageDollarValue(CARS), 790700);
})
 
 
// Exercise 4:
// ============
// Write a function: sanitizeNames() using compose that returns a list of lowercase and underscored names: e.g: sanitizeNames(["Hello World"]) //=> ["hello_world"].
 
const _underscore = _.replace(/\W+/g, '_'); //<-- leave this alone and use to sanitize
 
const sanitizeNames = _.map(
  _.compose(
    _underscore,
    _.toLower,
    _.prop('name')
  )
)
 
QUnit.test("Ex4: sanitizeNames", assert => {
  assert.deepEqual(sanitizeNames(CARS), ['ferrari_ff', 'spyker_c12_zagato', 'jaguar_xkr_s', 'audi_r8', 'aston_martin_one_77', 'pagani_huayra']);
})
 
 
 
// Bonus 1:
// ============
// Refactor availablePrices with compose.
const formatDollarValue = _.compose(
      formatMoney,
      _.prop('dollar_value')
    )
const availablePrices = _.compose(
  _.join(', '),
  _.map(formatDollarValue),
  _.filter(_.prop('in_stock'))
)
 
QUnit.test("Bonus 1: availablePrices", assert => {
  assert.deepEqual(availablePrices(CARS), '$700,000.00, $1,850,000.00');
})
 
// Bonus 2:
// ============
// Refactor to pointfree.
const append = _.flip(_.concat)
const fastestCar = _.compose(
  append(' is the fastest'),
  _.prop('name'),
  _.last,
  _.sortBy(_.prop('horsepower'))
)
 
QUnit.test("Bonus 2: fastestCar", assert => {
  assert.equal(fastestCar(CARS), 'Aston Martin One-77 is the fastest');
})