How Can I Efficiently Count the Frequency of Elements in a JavaScript Array?

Counting the Occurrences / Frequency of Array Elements

Counting the frequency of array elements is a common programming task, and JavaScript provides various methods to achieve this. One effective approach involves utilizing an object. Let's dive into a detailed solution.

Object-Based Method

Create an empty object to hold the counts.

const counts = {};

Iterate through each element in the original array.

for (const num of arr) {

For each element, check if it exists as a property in the counts object.

if (counts[num]) {

If the property exists, increment its value by 1.

  counts[num] += 1;

If the property doesn't exist, set its value to 1.

} else {
  counts[num] = 1;
}

Example

Consider the following input array:

[5, 5, 5, 2, 2, 2, 2, 2, 9, 4]

Using the object-based method, we get the following result:

{ 5: 3, 2: 5, 9: 1, 4: 1 }

Accessing Individual Counts

To access the count for a specific element, use the property name, which is the element itself.

console.log(counts[5]); // Output: 3
console.log(counts[2]); // Output: 5

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