javascript custom sorting function to place lower occurrence first

Question

Need to create a custom sort for an array --

-- first separate numbers by frequency --- subset numbers of having frequency 1 --- subset numbers of having frequency 2

partially sorted data - with respect to asc order of frequency - then we sort each subset of elements of having the same frequencey in non desc order

function cSort(arr) {
    if(typeof arr !== "undefined") {
        arr.sort(function(a, b) {
          return a - b;
        });

        return arr
    }
}

needs to satisfy the test cases

-- test 1 input [5, 3, 1, 2, 2, 4] output [1, 3, 4, 2, 2]

-- test 2 input [10, 8, 5, 5, 5, 5, 1, 1, 1, 4, 4] output [8, 4, 4, 1, 1, 1, 5, 5, 5, 5]

-- current jsfiddle 1 http://jsfiddle.net/6mekdn8h/

new fiddle 2 http://jsfiddle.net/6mekdn8h/1/

What about `5`, I believe the output should be `[1, 3, 4, 5, 2, 2]` isn't it? — Shidersz, Jun 11 '19 at 19:04
Possible duplicate of [sort by number of occurrence(count) in Javascript array](https://stackoverflow.com/questions/22010520/sort-by-number-of-occurrencecount-in-javascript-array) — Scath, Jun 11 '19 at 19:05
not sure why 5 is opted out -- but its not in the test result expected — The Old County, Jun 11 '19 at 19:06
[10, 8, 5, 5, 5, 5, 1, 1, 1, 4, 4] -- should output [8, 4, 4, 1, 1, 1, 5, 5, 5, 5] — The Old County, Jun 11 '19 at 19:09

Nina Scholz · Accepted Answer · 2019-06-11T19:51:28.667

1

You could take a sorting with the count of the occurences of each item.

var array = [5, 3, 1, 2, 2, 4].slice(1),
    hash = array.reduce((h, v, i) => (h[v] = (h[v] || 0) + 1, h), {});

array.sort((a, b) => hash[a] - hash[b] || a - b);

console.log(array);

edited Jun 11 '19 at 19:51

answered Jun 11 '19 at 19:21

Nina Scholz

376,160
25
347
392

http://jsfiddle.net/6mekdn8h/2/ test 2 input [10, 8, 5, 5, 5, 5, 1, 1, 1, 4, 4] output [8, 4, 4, 1, 1, 1, 5, 5, 5, 5] – The Old County Jun 11 '19 at 19:29
you could take only the rest without the first element. – Nina Scholz Jun 11 '19 at 19:43
whats the solution? – The Old County Jun 11 '19 at 19:45
so this is coming out at [8, 10, 4, 4, 1, 1, 1, 5, 5, 5, 5] -- instead of [8, 4, 4, 1, 1, 1, 5, 5, 5, 5] – The Old County Jun 11 '19 at 19:45
you could splice the larget item. – Nina Scholz Jun 11 '19 at 19:50
there is no 10 in the input my mistake – The Old County Jun 11 '19 at 19:50
the old is back. – Nina Scholz Jun 11 '19 at 19:51

javascript custom sorting function to place lower occurrence first

1 Answers1