ramda-compose.js

// Example Data
var 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.
var isLastInStock = function(cars) {
  var last_car = R.last(cars);
  return _.prop('in_stock', last_car);
};

isLastInStock = R.compose(R.prop('in_stock'), R.last);

// Exercise 2:
// ============
// use _.compose(), _.prop() and _.head() to retrieve the name of the first car
var nameOfFirstCar = R.compose(R.prop('name'), R.head);
var result = nameOfFirstCar(CARS);
console.log(result);

// Exercise 3:
// ============
// Use the helper function _average to refactor averageDollarValue as a composition
var _average = function(xs) { return R.reduce(R.add, 0, xs) / xs.length; }; // <- leave be

var averageDollarValue = function(cars) {
  var dollar_values = R.map(function(c) { return c.dollar_value; }, cars);
  return _average(dollar_values);
};

averageDollarValue = R.compose(_average, R.map(R.prop('dollar_value')));
averageDollarValue(CARS);

var toLowerCase = R.curry(function(what) {
 return what.toLowerCase(); 
});

// Exercise 4:
// ============
// Write a function: sanitizeNames() using compose that returns a list of lowercase and underscored names: e.g: sanitizeNames(["Hello World"]) //=> ["hello_world"].

var _underscore = R.replace(/\W+/g, '_'); //<-- leave this alone and use to sanitize

var sanitizeNames = R.map(R.compose(_underscore, toLowerCase, R.prop('name')));
sanitizeNames([{name: "Hello World", horsepower: 660, dollar_value: 700000, in_stock: true}]);

// Bonus 1:
// ============
// Refactor availablePrices with compose.

var formatMoney = function(x) {
  return x+100;
};

var availablePrices = function(cars) {
  var available_cars = R.filter(_.prop('in_stock'), cars);
  return available_cars.map(function(x){
    return x.dollar_value + 50;
  }).join(', ');
};

availablePrices = R.compose(R.join(','), R.map(R.compose(formatMoney, R.prop('dollar_value'))), R.filter(R.prop('in_stock')));

// Bonus 2:
// ============
// Refactor to pointfree. Hint: you can use _.flip()

var fastestCar = function(cars) {
  var sorted = R.sortBy(function(car){ return car.horsepower }, cars);
  var fastest = R.last(sorted);
  return fastest.name + ' is the fastest';
};

var sortBy = R.sortBy(R.prop('horsepower'));
var fasted = R.last;
fastedCar = R.compose(R.prop('name'), R.compose(fasted, sortBy));

fastedCar(CARS) + ' is the fastest';