How to remove duplicates from an array of objects using JavaScript ?

In this article, we are given an array of objects and the task is to remove the duplicate object element from the array list.

These are the methods to solve this problem which are discussed below:

Method 1: Using one of the keys as an index

• A temporary array is created that stores the objects of the original array using one of its keys as the index.
• Any of the object properties can be used as a key. The key is extracted from the object and used as the index of the new temporary array.
• The object is then assigned to this index.
• This approach will remove the duplicate objects as only one of each object of the original array will get assigned to the same index. 

Example: This example is the implementation of the above-explained method.

Javascript

function removeDuplicates() {

    // Create an array of objects
    books = [
        { title: "C++", author: "Bjarne" },
        { title: "Java", author: "James" },
        { title: "Python", author: "Guido" },
        { title: "Java", author: "James" },
    ];

    // Declare a new array
    let newArray = [];

    // Declare an empty object
    let uniqueObject = {};

    // Loop for the array elements
    for (let i in books) {

        // Extract the title
        objTitle = books[i]['title'];

        // Use the title as the index
        uniqueObject[objTitle] = books[i];
    }

    // Loop to push unique object into array
    for (i in uniqueObject) {
        newArray.push(uniqueObject[i]);
    }

    // Display the unique objects
    console.log(newArray);
}
removeDuplicates();

Output

[
  { title: 'C++', author: 'Bjarne' },
  { title: 'Java', author: 'James' },
  { title: 'Python', author: 'Guido' }
]

Method 2: Converting the array to a Set to remove the duplicates

• A Set object holds only unique values of any type. This property can be used to store only the objects that are unique in the array.
• Each object of the array is first converted into a JSON-encoded string using the JSON.stringify method.
• The JSON-encoded string is then mapped to an array using the map() method. A new set is created by passing this array to the new set constructor.
• This step will remove all the duplicate elements as the JSON-encoded strings will be the same for the same elements.
• The set is then converted to an Array using the from() method, passing the set as a parameter. This array will not have duplicated objects. 

Example: In this example, we will remove the duplicate values from an array of objects by converting the array to a set to remove the duplicates.

Javascript

function removeDuplicates() {

    // Create an array of objects
    books = [
        { title: "C++", author: "Bjarne" },
        { title: "Java", author: "James" },
        { title: "Python", author: "Guido" },
        { title: "Java", author: "James" },
    ];

    jsonObject = books.map(JSON.stringify);
    uniqueSet = new Set(jsonObject);
    uniqueArray = Array.from(uniqueSet).map(JSON.parse);

    console.log(uniqueArray);
}
removeDuplicates();

Output

[
  { title: 'C++', author: 'Bjarne' },
  { title: 'Java', author: 'James' },
  { title: 'Python', author: 'Guido' }
]

Method 3: Using filter() and includes() Method

In this method, we will filter the data from the book and include the data which is not repeated in a new array.

Example: This example is the implementation of the above-explained method.

Javascript

const books = [
    { title: "C++", author: "Bjarne" },
    { title: "Java", author: "James" },
    { title: "Python", author: "Guido" },
    { title: "Java", author: "James" },
];

const ids = books.map(({ title }) => title);
const filtered = books.filter(({ title }, index) =>
    !ids.includes(title, index + 1));

console.log(filtered);

Output

[
  { title: 'C++', author: 'Bjarne' },
  { title: 'Python', author: 'Guido' },
  { title: 'Java', author: 'James' }
]

Method 4: Using filter() and findIndex() Method

In this method, we will filter() the array by using the Array.findIndex() method to return the first index of the element in a given array that satisfies the provided testing function (passed in by the user while calling)

Example: This example is the implementation of the above-explained method.

Javascript

const books = [
    { title: "C++", author: "Bjarne" },
    { title: "Java", author: "James" },
    { title: "Python", author: "Guido" },
    { title: "Java", author: "James" },
];

const unique = books.filter((obj, index) => {
    return index === books.findIndex(o => obj.title === o.title);
});

console.log(unique);

Output

[
  { title: 'C++', author: 'Bjarne' },
  { title: 'Java', author: 'James' },
  { title: 'Python', author: 'Guido' }
]

Method 5: Using Lodash _.uniq() method

In this method, we are using _.uniq() method which returns the unique value present in the given array.

Example: This example is the implementation of the above-explained method.

Javascript

// Requiring the lodash library
const _ = require("lodash");

// Use of _.uniq()
// method
let arr = _.uniq([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x');

// Printing the output
console.log(arr);

Output:

 [{ 'x': 1 }, { 'x': 2 }]