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// 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';
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