JavaScript- Count Frequencies in an Array Last Updated : 19 Nov, 2024 Comments Improve Suggest changes Like Article Like Report These are the following ways to count the frequency:1. Using Object (Efficient for Small to Moderate Arrays)We use JavaScript Objects to store frequencies, we iterate over the array using the forEach() method. For each element, we check if the element already exists as a key in the res object. If it does, we increment its count; if not, we initialize it to 1. JavaScript const a = [4, 2, 3, 4, 3, 2, 4, 1, 3, 2]; let res = {}; a.forEach(e => { res[e] = (res[e] || 0) + 1; }); console.log(res); 2. Using Map (Easiest and Efficient for All Types of Arrays)Here, we use a Map to store the frequency of each element. We iterate over the array using forEach() and use the get() method to check if the element is already in the Map. JavaScript const a1 = [4, 2, 3, 4, 3, 2, 4, 1, 3, 2]; let res = new Map(); a1.forEach(e => { res.set(e, (res.get(e) || 0) + 1); }); console.log(Object.fromEntries(res)); Output{ '1': 1, '2': 3, '3': 3, '4': 3 } 3. Using reduce() with Map (Similar to 2nd)This approach uses the reduce() method, which is typically used to accumulate results. We can also use reduce with Objects. JavaScript const a = [4, 2, 3, 4, 3, 2, 4, 1, 3, 2]; let res = a.reduce((acc, e) => { acc.set(e, (acc.get(e) || 0) + 1); return acc; }, new Map()); console.log(res); Output{ '1': 1, '2': 3, '3': 3, '4': 3 } 4. Using for...of Loop Object (Similar to 2nd, only loop is different)This approach uses the for...of loop to iterate through each element of the array and store frequencies in Map. We can also use this with Object. JavaScript const a = [4, 2, 3, 4, 3, 2, 4, 1, 3, 2]; let res = new Map(); for (const e of a) { res.set(e, (res.get(e) || 0) + 1); } console.log(res); Output{ '1': 1, '2': 3, '3': 3, '4': 3 } Comment More infoAdvertise with us Next Article JavaScript- Count Frequencies in an Array M meetahaloyx4 Follow Improve Article Tags : JavaScript Web Technologies DSA javascript-array Similar Reads Count Frequency of an Array Item in JavaScript Here are the different approaches to count the frequency of an Array Item in JavaScriptUsing a Loop and CounterThis 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.JavaScriptcon 2 min read JavaScript - Counting Frequencies of Array Elements Here are the various approaches to count the frequencies of array elements in JavaScript.Using an Object (Simple and Efficient)This is the most common approach for counting frequency in an array. Each array element becomes a key in the object, and its value is incremented as the element appears.Java 2 min read Count indices with Specific Frequency in Array Range Given an array of N elements and num queries, In each query, you are given three numbers L, R, and K and you have to tell, how many indexes are there in between L and R(L <= i <= R) such that the frequency of a[i] from index i to n-1 is K. Follow 0-based indexing Examples: Input: N = 5, num = 11 min read Frequency of an element in an array Given an array, a[], and an element x, find a number of occurrences of x in a[].Examples: Input : a[] = {0, 5, 5, 5, 4} x = 5Output : 3Input : a[] = {1, 2, 3} x = 4Output : 0Unsorted ArrayThe idea is simple, we initialize count as 0. We traverse the array in a linear fashion. For every element that 9 min read Counting frequencies of array elements Given an array which may contain duplicates, print all elements and their frequencies. Examples: Input : arr[] = {10, 20, 20, 10, 10, 20, 5, 20}Output : 10 3 20 4 5 1Input : arr[] = {10, 20, 20}Output : 10 1 20 2 A simple solution is to run two loops. For every item count number of times, it occurs. 15+ min read Like