readme.md

Challenge: Car Mileage Analysis

Instructions

You are given an array of car objects, each containing information about a car's make, model, year, and mileage. Your goal is to perform some analysis on the car mileage data using high order array methods.

Implement a function called analyzeCarMileage which takes in an array of car objects and performs the following tasks:

1. Calculate the average mileage of all cars.
2. Find the car with the highest mileage.
3. Find the car with the lowest mileage.
4. Calculate the total mileage of all cars combined.

The function should return an object containing the calculated values as properties.

Here is an object that you can use to test your function in the run file:

const cars = [
  { make: 'Toyota', model: 'Camry', year: 2020, mileage: 30800 },
  { make: 'Honda', model: 'Civic', year: 2019, mileage: 32000 },
  { make: 'Chevrolet', model: 'Impala', year: 2021, mileage: 17500 },
  { make: 'Audi', model: 'R8', year: 2020, mileage: 13000 },
  { make: 'Tesla', model: 'Model 3', year: 2018, mileage: 50000 },
];

Function Signature

/**
 * Analyzes car mileage data using high order array methods.
 * @param {Array} cars - An array of car objects.
 * @returns {Object} - An object containing calculated values.
 */
function analyzeCarMileage(cars: object[]): object;

Each car object will have the following properties:

• make: The make of the car (string).
• model: The model of the car (string).
• year: The year the car was manufactured (number).
• mileage: The mileage of the car (number).

Examples

const cars = [
  { make: 'Toyota', model: 'Corolla', year: 2020, mileage: 25000 },
  { make: 'Honda', model: 'Civic', year: 2019, mileage: 30000 },
  { make: 'Ford', model: 'Mustang', year: 2021, mileage: 15000 },
];

const analysis = analyzeCarMileage(cars);
console.log(analysis);
// Output:
// {
//   averageMileage: 23333.33,
//   highestMileageCar: { make: "Honda", model: "Civic", year: 2019, mileage: 30000 },
//   lowestMileageCar: { make: "Ford", model: "Mustang", year: 2021, mileage: 15000 },
//   totalMileage: 70000
// }

Constraints

• The input array cars will contain at most 100 car objects.
• Each car object's mileage property will be a positive integer.
• Result should be rounded to 2 decimal places.

Hints

• You can use the reduce method for most of the calculations.

Solution

Click to view solution

function analyzeCarMileage(cars) {
  const totalMileage = cars.reduce((sum, car) => sum + car.mileage, 0);
  const averageMileage = totalMileage / cars.length;
  const highestMileageCar = cars.reduce(
    (highest, car) => (car.mileage > highest.mileage ? car : highest),
    cars[0]
  );
  const lowestMileageCar = cars.reduce(
    (lowest, car) => (car.mileage < lowest.mileage ? car : lowest),
    cars[0]
  );

  return {
    averageMileage: parseFloat(averageMileage.toFixed(2)),
    highestMileageCar,
    lowestMileageCar,
    totalMileage,
  };
}

Explanation

• Create a variable totalMileage and initialize it to the result of calling the reduce method on the cars array. The accumulator should be the sum of the accumulator and the car's mileage. The initial value of 0 will be used as the initial value of the accumulator.
• Create a variable averageMileage and initialize it to the result of dividing totalMileage by the length of the cars array.
• Create a variable highestMileageCar and initialize it to the result of calling the reduce method on the cars array. The accumulator should be the car with the highest mileage. The initial value of cars[0] will be used as the initial value of the accumulator.
• Create a variable lowestMileageCar and initialize it to the result of calling the reduce method on the cars array. The accumulator should be the car with the lowest mileage. The initial value of cars[0] will be used as the initial value of the accumulator.
• Return an object containing the calculated values. Round the averageMileage to 2 decimal places using the toFixed method and convert it to a number using the parseFloat method.

I know that reduce can be a little tough to understand, so let's really break it down for the highestMileageCar variable. Here is the code again for reference:

const highestMileageCar = cars.reduce(
  (highest, car) => (car.mileage > highest.mileage ? car : highest),
  cars[0]
);

1. reduce takes two main arguments: a function and an initial value. The initial value is set to cars[0], which is the first car in the list.
2. The function takes two parameters: highest and car. highest initially holds the first car, and car is the next car in the list.
3. For each car, the function compares the mileage of the current car car.mileage with the mileage of the car that was thought to be the highest so far highest.mileage.
4. If the current car's mileage is greater, we replace the value of highest with the current car.
5. If the current car's mileage is not greater, we stick with the car we thought was the best so far (highest).
6. This process repeats for each car in the list.

Whatever we return from the callback for the reduce method will be the new value of the accumulator.

Test Cases

test('Analyzing Car Mileage Data', () => {
  const cars = [
    { make: 'Toyota', model: 'Corolla', year: 2020, mileage: 25000 },
    { make: 'Honda', model: 'Civic', year: 2019, mileage: 30000 },
    { make: 'Ford', model: 'Mustang', year: 2021, mileage: 15000 },
  ];

  const analysis = analyzeCarMileage(cars);

  expect(analysis.averageMileage).toBeCloseTo(23333.33);
  expect(analysis.highestMileageCar).toEqual({
    make: 'Honda',
    model: 'Civic',
    year: 2019,
    mileage: 30000,
  });
  expect(analysis.lowestMileageCar).toEqual({
    make: 'Ford',
    model: 'Mustang',
    year: 2021,
    mileage: 15000,
  });
  expect(analysis.totalMileage).toBe(70000);
});

Feel free to add more test cases to verify the correctness of your analyzeCarMileage function.