Count Frequency of an Array Item in JavaScript

Count Frequency of an Array Item in JavaScript

Last Updated : 14 Nov, 2024

Here are the different approaches to count the frequency of an Array Item in JavaScript

Using a Loop and Counter

This is the most basic and efficient approach when you want to find the frequency of a single item. You simply loop through the array and count how many times the item appears.

JavaScript

const frequency = (arr, item) => {
    let count = 0;
    for (let i = 0; i < arr.length; i++) {
        if (arr[i] === item) {
            count++;
        }
    }
    return count;
};

const a = [1, 2, 3, 2, 1, 2, 3, 1];
console.log(frequency(a, 2));

Output

Using filter() Method

You can filter the array to only include occurrences of the target element and then return the length of the filtered array.

JavaScript

const frequency = (arr, item) => {
    return arr.filter(x => x === item).length;
};

const a = [1, 2, 3, 2, 1, 2, 3, 1];
console.log(frequency(a, 2));

Output

Using reduce() Method

The reduce() method can also be used to accumulate the frequency of a single item by checking each element in the array.

JavaScript

const frequency = (arr, item) => {
    return arr.reduce((count, x) => x === item ? count + 1 : count, 0);
};

const a = [1, 2, 3, 2, 1, 2, 3, 1];
console.log(frequency(a, 2));

Output

Using an Object (for Larger Arrays)

If you're working with larger arrays and you want to count occurrences efficiently, an object can be used to store counts of all items. But you can optimize it for a single item by simply counting the target item.

JavaScript

const frequency = (a, item) => {
    const o = {};
    a.forEach(x => {
        if (x === item) {
            o[item] = (o[item] || 0) + 1;
        }
    });
    return o[item] || 0;
};

const a = [1, 2, 3, 2, 1, 2, 3, 1];
console.log(frequency(a, 2));

Output

Count Frequency of an Array Item in JavaScript

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