Mastering JavaScript: How to Sort Arrays by Most Frequent Values Descending Order

Learn how to create a JavaScript function that sorts and returns an array of the most repeated values in `descending order`. Follow our step-by-step guide!
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This video is based on the question https://stackoverflow.com/q/65448198/ asked by the user 'DjBillje Official' ( https://stackoverflow.com/u/14506531/ ) and on the answer https://stackoverflow.com/a/65448281/ provided by the user 'Janó Gáll' ( https://stackoverflow.com/u/13749743/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering JavaScript: How to Sort Arrays by Most Frequent Values Descending Order

In the world of programming, arrays are one of the most commonly used data structures. From sorting to filtering data, the functionality they offer is vast. A common question among JavaScript developers is how to identify and sort the most repeated values within an array. In this guide, we will tackle the problem of sorting an array's values by their repetition in descending order, using a practical example to illustrate our solution.

The Problem

Imagine you have the following array:

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

The goal is to write a function that processes this array and returns the values sorted by the number of times they appear, in descending order. For our example array, the expected output would be:

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

This output ranks bill as the most frequent value, followed by max, and then anup. To achieve this, you might have heard of nested for loops, but there are better and more efficient methods available. Let’s explore a straightforward way to accomplish this task.

The Solution

We can use the JavaScript Map object to count the occurrences of each value in the array. Then, we can sort these values based on their counts. Below, we will break down the solution step-by-step.

Step 1: Initialize a Map

Maps in JavaScript allow us to associate values with keys. We will use this feature to keep track of how many times each string appears in our array.

Step 2: Count the Occurrences

We will iterate over the array and use the Map to record the counts. For each item in the array, we will check if it already exists in the Map; if it does, we increase its count; if not, we initialize it with a count of one.

Step 3: Sort the Values

Once we have the counts, we will convert our Map entries back into an array and sort it based on the frequency of occurrences in descending order.

Step 4: Return the Result

Finally, we will extract the sorted values into a new array to return our desired result.

Here's the complete code that implements the above steps:

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

Code Breakdown

const array = [...]: The initial array containing strings.

countMap: This Map will store the string as the key and its count as the value.

forEach(item => {...}): We iterate through the array, updating the count in the Map.

.sort((a, b) => b[1] - a[1]): This sorts the Map entries by the count property in descending order.

.map(entry => entry[0]): Finally, we return just the keys (the sorted strings) as an array.

Conclusion

By using a Map and the built-in array methods, we efficiently calculate and sort the occurrences of items in a JavaScript array. This method avoids the complexities and performance issues associated with nested loops, resulting in cleaner and more efficient code.

This function can be very useful in data analysis, creating reports, or anytime you need to identify trending items in a dataset. Try implementing this function on your own different datasets and observe how it performs!

Happy coding!

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