Скачать или смотреть How to Group By Arrays of Objects in JavaScript Efficiently

Discover a simple method to `group arrays` of objects in JavaScript by using the `reduce` function, along with clear examples and code snippets.
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Group By Arrays of Objects in JavaScript

When working with complex data in JavaScript, particularly arrays of objects, you might often need to group these objects by certain criteria for better organization and manipulation. In this post, we will tackle the problem of grouping an array of objects based on their properties, specifically by their AdminLevel. This case study focuses on a real-world example and provides a detailed approach to implement the solution.

The Problem Explained

You have an array of objects that represent various entities such as cities and districts relevant to administrative levels. Here’s a snippet of what the data structure looks like:

[[See Video to Reveal this Text or Code Snippet]]

The objective is to group these objects so that entities that share a common ParentId under AdminLevel 4 are associated with their specific Id from AdminLevel 6. The desired output structure should be similar to this:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To achieve this grouping, we will leverage the reduce function, which is powerful for transforming an array into a singular object (or array) based on certain conditions.

Step-by-Step Implementation

Filter Relevant Admin Levels: Start by filtering the original array to get only the entries for AdminLevel 4 and AdminLevel 6.

Reduce to Group: Use the reduce method to build an accumulator object. The key will be determined based on the AdminLevel. If the item has AdminLevel 4, its Id will be the key; for AdminLevel 6, the key will be its ParentId.

Push IDs to Selected: For entries with AdminLevel 6, push their Ids into the Selected array of their corresponding AdminLevel 4 entry.

Here’s the Code for the Implementation:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code:

Filtering: The filter() method narrows the dataset to just the relevant AdminLevel items.

Reducing: The reduce() function builds an object where each key corresponds to the ParentId of AdminLevel 6 entries, and the value is an object containing the Id, AdminLevel, and an array for Selected.

Final Output: Object.values() retrieves an array of the grouped results.

Conclusion

Grouping arrays of objects by certain properties may seem daunting at first, but JavaScript's functional programming patterns make it manageable and efficient. By understanding how to filter and reduce your data, you can easily manipulate arrays into the structure you need for your application.

Feel free to experiment with the code and adjust it as necessary to suit your specific needs. Happy coding!