Скачать или смотреть How to Remove Duplicate Keys from an Array of Objects in JavaScript

Learn how to effectively eliminate duplicate keys from an array of objects in JavaScript while keeping the last occurrence of each key.
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Dealing with Duplicate Keys in JavaScript Arrays

If you work with JavaScript, you might encounter situations where you have an array of objects, and some of those objects contain the same key. In scenarios where you need to keep only the last occurrence of an object by its key, the challenge lies in effectively filtering out the earlier instances while preserving the latest one.

The Problem Statement

Imagine you have the following array of objects:

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Here, many objects share the same keys (d0, d3, etc.). Your goal is to remove all objects with the same key except for the last occurrence. For instance, after processing the array, you want to obtain:

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The Solution

To solve this problem, you can use various approaches. Below, we will explore two effective methods: using the reduceRight function and using Object.assign.

Method 1: Using reduceRight with a Closure

One of the most efficient methods to achieve this is by utilizing the reduceRight function combined with a closure to maintain a Set object that tracks the keys you've encountered.

Here’s how you can implement this:

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Breakdown of the Code:

Initialization: We initialize a Set (s) which keeps track of the keys we have already added.

Iterate from Right: The reduceRight function will process the array from its last element to the first.

Check Set for Existing Key: If the key from the current object already exists in the set, we skip it. Otherwise, we add the new key to the set and include the object in the accumulator array.

Example Code:

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Method 2: Cumulative Object using Object.assign

In cases where you prefer to create a cumulative object while preserving the last key values, you might want to use Object.assign in conjunction with reduce.

Here's how you would do that:

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Performance Optimized Version

To further enhance performance, you can iterate from the end of the list and escape if the key already exists, using:

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Conclusion

In summary, these methods let you efficiently manage arrays of objects in JavaScript by removing duplicate keys while maintaining the latest values. Depending on your requirement—whether you want a filtered array or a cumulative object—you can select the method that best fits your needs.

By mastering these techniques, you can enhance your array manipulation skills in JavaScript and tackle similar challenges with ease.