Most Efficient Method to groupBy on an Array of Objects in JavaScript

Grouping data on the basis of some specific properties is a common task in JavaScript. Whether you’re arranging user data, categorizing products, or handling API responses, you may find the need to group data. In this article, we will explore different ways to group an array of objects by a property in JavaScript.

Table of Contents:

• The Problem
• Different Approaches to Grouping Data
  • Method 1: Using a for Loop
  • Method 2: Using reduce() Method
  • Method 3: Create a Reusable groupBy() function
• How to Group Objects By Multiple Keys
• Performance Comparison
• Conclusion

The Problem

The problem is that you have to group an array of objects by property in JavaScript. Let’s understand the problem with the help of an example:

Input:

const employees = [
  { name: "IntellipaatE1", department: "Engineering" },
  { name: "IntellipaatE2", department: "HR" },
  { name: "IntellipaatE3", department: "Engineering" },
  { name: "IntellipaatE4", department: "Marketing" },
];

You have an array of objects that contain the data of employees working at Intellipaat. Your goal is to group these Intellipaat employees by their department. Thus, the Output looks like this:

Expected Output:

{
  Engineering: [
    { name: "IntellipaatE1", department: "Engineering" },
    { name: "IntellipaatE3", department: "Engineering" }
  ],
  HR: [
    { name: "IntellipaatE2", department: "HR" }
  ],
  Marketing: [
    { name: "IntellipaatE4", department: "Marketing" }
  ]
}

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Different Approaches to Grouping Data

Grouping an array of objects by some specific properties is important in JavaScript. Let’s discuss all the methods one by one:

Method 1: Using a for Loop

The simplest and traditional method to group objects by property is by using a for loop. The only disadvantage of this method is that you have to write more lines of code.

Example:

Output:

Explanation: In this example, a traditional for loop is used to group an array of objects in JavaScript based on a property. Here, you can perform grouping by their single property called department.

Method 2: Using reduce() Method

A modern and functional approach to grouping objects is by using the reduce() method in JavaScript. It is shorter as compared to the previous for loop method.

Example:

Output:

Explanation: Here, you are using the reduce() method to perform the grouping of objects.

Method 3: Create a Reusable groupBy() function

To perform the grouping of objects more than once, you can create a groupBy() function by writing the following lines of code:

Example:

Output:

Explanation: In this example, the employees array has employee objects with name and department properties. The reduce() method is used to iterate over an array of objects and checks for the given property to exist in each object or not. If the property value does not exist in acc, then it creates an empty array and pushes the current object into the group.

How to Group Objects By Multiple Keys

Sometimes, you find a need to group the objects by more than one property. Here is the way to do it:

Example:

Output:

Explanation: In this example, you are grouping an object not with a single property but with multiple properties, like the department and the role.

Performance Comparison

Here is the performance comparison between all the methods that are used to perform the grouping of objects in JavaScript:

Conclusion

Grouping objects by the property is important for working with structured data in JavaScript. You have various methods for grouping objects by property in JavaScript, from traditional for loops to the modern reduce() method. By learning these methods, you will be able to control data efficiently.

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