Counting array elements and sort descending by count

Question

Array:

5, 5, 5, 9, 4, 2, 2, 2, 2, 2, 3, 3, 3, 3

Ideal Output:

2, 3, 5, 9, 4

PHP made this easy with array_count_values() and arsort(), but javascript is proving a little tougher. Any help?

Also, what about returning it containing the counts as well? For future needs

Check out the accepted answer [here](http://stackoverflow.com/questions/1960473/unique-values-in-an-array). Then, of course, there is a .sort() method. — Xynariz, Aug 02 '13 at 01:18
Did you mean to say "descending by count"? The `2` is the most frequent occurrence... — Floris, Aug 02 '13 at 01:19
@Xynariz Its not just removing duplicates and sorting. Read the post correctly — GameDevGuru, Aug 02 '13 at 01:23
@GameDevGuru Sorry, the question wasn't clear to me. I wasn't aware of the fact that you were looking for the order to be by counts (it's mentioned in your subject, but not your question). Also, how do you want it sorted if there is a tie (in your example, there is only one 4 and only one 9)? — Xynariz, Aug 02 '13 at 01:25
http://phpjs.org/functions/array_count_values/ phpjs can simulate the same function which in php. it may help you. — bystander, Aug 02 '13 at 01:30
@Blender If i were to use array_count_values, i would need to sort descending through the count values. `.sort()` doesn't accept objects — GameDevGuru, Aug 02 '13 at 01:59

Paul S. · Accepted Answer · 2013-08-03T12:05:18.467

4

Count unique entries, create an array of uniques, then sort based upon counts

function count(arr) { // count occurances
    var o = {}, i;
    for (i = 0; i < arr.length; ++i) {
        if (o[arr[i]]) ++o[arr[i]];
        else o[arr[i]] = 1;
    }
    return o;
}

function weight(arr_in) { // unique sorted by num occurances
    var o = count(arr_in),
        arr = [], i;
    for (i in o) arr.push(+i); // fast unique only
    arr.sort(function (a, b) {
        return o[a] < o[b];
    });
    return arr;
}

weight([1, 3, 3, 5, 5, 5, 2, 2, 2, 2]);
// one 1, two 3s, three 5s, four 2s
// [2, 5, 3, 1]

You example has both one 9 and one 4, so if you want the order defined, more work would be necessary. Otherwise;

weight([5, 5, 5, 9, 4, 2, 2, 2, 2, 2, 3, 3, 3, 3]);
// [2, 3, 5, 4, 9]

To produce an Array of Objects

function weight(arr_in) { // unique sorted by num occurances
    var o = count(arr_in),
        arr = [], i;
    for (i in o) arr.push({value: +i, weight: o[i]}); // fast unique only
    arr.sort(function (a, b) {
        return a.weight < b.weight;
    });
    return arr;
}

var result = weight([5, 5, 5, 9, 4, 2, 2, 2, 2, 2, 3, 3, 3, 3]);
/* [
    {"value": 2, "weight": 5},
    {"value": 3, "weight": 4},
    {"value": 5, "weight": 3},
    {"value": 4, "weight": 1},
    {"value": 9, "weight": 1}
] */

Now, to get the value at index i, you do result[i].value, and for it's weighting result[i].weight.

edited Aug 03 '13 at 12:05

answered Aug 02 '13 at 01:25

Paul S.

64,864
9
122
138

Could i also get output with count of each value? For future reference. – GameDevGuru Aug 02 '13 at 02:08
No i mean `2:5, 3:4, 5:3, 9:1, 4:1` – GameDevGuru Aug 02 '13 at 02:25
I've spent hours trying, but I can't seem to modify it properly. – GameDevGuru Aug 02 '13 at 14:20
You-re not being very clear - `2:5, 3:4, 5:3, 9:1, 4:1` does not make sense; do you mean the _Object_ `{2: 5, 3: 4, 4: 1, 5: 3, 9: 1}`? This is what is `return`ed by `count`. Alternatively, perhaps you want an _Array_ of _Objects_ like `[{value: 2, weight: 5}, {value: 3, weight: 4}/*, etc*/]` with which you would always thereafter need to specify whether you wanted the value or the weight. In my opinion using the _Object_ is easier as you can have it as a dictionary lookup if you ever wanted and does not require more code :) – Paul S. Aug 02 '13 at 16:09
Yea i would like it as a sorted array of objects so it's easier to iterate through. I come from PHP so i'm having a little trouble with this. – GameDevGuru Aug 03 '13 at 06:18
Count is working properly, it just wont sort by the count. I've tried everything! – GameDevGuru Aug 03 '13 at 15:56
The integers have various lengths. `eg: 333223, 2333,23444455` etc I believe that's making a difference for sort – GameDevGuru Aug 03 '13 at 16:11
I fixed it. `return b.weight - a.weight;` – GameDevGuru Aug 03 '13 at 20:38

Counting array elements and sort descending by count

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