Javascript: sort elements in array by their frequencies

Question

There is an array whose elements are same items in random order. I want to reorder the array such that items with high frequencies appear first and then the items with the lowest frequencies appear last.

Basically, what would be the code to return the result below?

const a = [1,5,3,3,2,3,4,3,3,2,4,4,4];

const result = [3,3,3,3,3,4,4,4,4,2,2,1,5];

Thanks a lot in advance!

Answer 1

Calculate the frequency and then sort the array based on the frequency:

let a = [1,5,3,3,2,3,4,3,3,2,4,4,4];

const freq = a.reduce((c, v) => (c[v] = (c[v] || 0) + 1, c), {});

a.sort((x, y) => freq[y]-freq[x] || y-x);

console.log(a);