How Can I Group JavaScript Objects by Key Using the `reduce()` Method?

Grouping Objects by Key Using JavaScript

Grouping an array of objects by a specific key is a common task in programming, especially when working with data sets. One efficient way to achieve this is through the reduce() method.

In JavaScript, you can follow these steps:

1. Declare an array of objects: Let's say you have an array of car objects, similar to the example provided in the question:

const cars = [
    { make: 'audi', model: 'r8', year: '2012' },
    { make: 'audi', model: 'rs5', year: '2013' },
    { make: 'ford', model: 'mustang', year: '2012' },
    { make: 'ford', model: 'fusion', year: '2015' },
    { make: 'kia', model: 'optima', year: '2012' },
];

2. Initialize an object as the accumulator: Create an empty object that will serve as the accumulator for the reduce() method. This object will store the grouped values.

const groupedCars = {};

3. Use reduce() to iterate over the array: Employ the reduce() method on the cars array to iterate over each object. The reduce() function takes two arguments:

• accumulator: The object created in step 2.
• currentElement: The current object being iterated over.

4. Add objects to the accumulator: Within the reduce() method, check if the current make property exists as a property in the accumulator object. If it does not exist, create a new array at that property. Then, push the currentElement into the created array. This process effectively groups objects based on their make.

const groupedCars = cars.reduce((accumulator, currentElement) => {
  const make = currentElement.make;

  if (!accumulator[make]) {
    accumulator[make] = [];
  }

  accumulator[make].push(currentElement);

  return accumulator;
}, {});

5. Return the grouped object: The reduce() method returns the accumulated object, which contains the grouped values.
6. Log the grouped result: You can log the grouped object to the console to verify the output.

console.log(groupedCars);

This approach uses vanilla JavaScript and provides a structured way to group objects based on a specified key, creating a new object with the grouped values.

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