How to Group Nested Arrays in JavaScript

Learn how to effectively group nested arrays in JavaScript with popular methods including Vanilla JavaScript and Lodash. Explore code examples and step-by-step explanations.
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How to Group Nested Arrays in JavaScript

If you're working with arrays in JavaScript, you may find yourself needing to process and manipulate data structures in various ways. One common challenge developers face is grouping nested arrays by their first elements. In this post, we’ll dive into how to achieve this, whether using vanilla JavaScript or the popular Lodash library.

Understanding the Problem

Let’s say you have a nested array structured like this:

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Your goal is to transform this into a more meaningful structure, such as:

An object:

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Or an array of arrays:

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Solution Using Lodash

Lodash makes it easy to work with arrays and objects, thanks to its powerful utility functions. Here’s how to group your array using Lodash:

Step 1: Import Lodash

First, ensure you include Lodash in your project. You can add it using a CDN:

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Step 2: Grouping the Array

Now, you can use the following code snippet to achieve your desired result:

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In this code:

groupBy(array, head) groups the elements by their first value, while head extracts that first value.

mapValues() takes the grouped results and transforms them into arrays of the second values using map(arr, last).

Solution Without Lodash

For those who prefer a vanilla JavaScript approach, you can achieve this using the reduce method alongside a Map. Here's how:

Step 1: Grouping with Reduce

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Why Use a Map?

Using a Map has its advantages:

It maintains the order of insertion.

It can store key-value pairs where keys are of any type (even objects).

Conclusion

Grouping nested arrays in JavaScript can be done seamlessly with both Lodash and vanilla JavaScript. By understanding these methods and implementing them in your projects, you can effectively organize your data and streamline your coding processes.

Feel free to experiment with these examples and adapt them to your unique needs! Happy coding!