How to get most frequent/occurring element in an array

Question

I am currently being faced with this problem where I am trying to find the most occurring or frequent element in an array.

For example:

const arr = [1,2,1,1,1,2,2,2,1] (Most occuring is: 1)

Follow up: What if I want to get the second-most occurring element?

Here's my solution:

function returnMostOccurring(arr) {
   const obj = {};
   arr.forEach(item => {
      if(!obj[item]) obj[item] = 1;
      else obj[item]++;
   })

   const res =  Object.entries(obj).sort((a,b) => b[1]-a[1]);
   return res.shift();
}

I figured this is not the most optimal way to solve this problem (O(nLogN) time complexity)

What is the best way to handle this kind of use case?

If solution will only using `javascript` then, it's fine? – Ahmed Ali Nov 27 '19 at 08:09 — Ahmed Ali, Nov 27 '19 at 08:09
@AhmedAli I'm looking for javascript only .. – TechnoCorner Nov 27 '19 at 08:51 — TechnoCorner, Nov 27 '19 at 08:51

Nina Scholz · Answer 1 · 2019-11-27T08:56:10.747

You could take a single loop with a variable for the element with the actual max count and an object for keeping the counts of the elements.

function mostOccurringElement(array) {
    var max = array[0],
        counter = {},
        i = array.length,
        element;
    
    while (i--) {
        element = array[i];
        if (!counter[element]) counter[element] = 0;
        counter[element]++;
        if (counter[max] < counter[element]) max = element;
    }
    return max;
}

const array = [1, 2, 1, 1, 1, 2, 2, 2, 1];

console.log(mostOccurringElement(array));

How to get most frequent/occurring element in an array

1 Answers1