sort by number of occurrence(count) in Javascript array

Question

I am new to Jquery and Javascript. Can someone please help me with Jquery sorting based on number of occurrence(count) in array. I tried various sorting methods but none of them worked.

I have an array in Javascript which is

allTypesArray = ["4", "4","2", "2", "2", "6", "2", "6", "6"]

// here  2 is printed four times, 6 is printed thrice, and 4 is printed twice

I need output like this

newTypesArray = ["2","6","4"]

I tried

function array_count_values(e) {
var t = {}, n = "",
    r = "";
var i = function (e) {
    var t = typeof e;
    t = t.toLowerCase();
    if (t === "object") {
        t = "array"
    }
    return t
};
var s = function (e) {
    switch (typeof e) {
    case "number":
        if (Math.floor(e) !== e) {
            return
        };
    case "string":
        if (e in this && this.hasOwnProperty(e)) {
            ++this[e]
        } else {
            this[e] = 1
        }
    }
};
r = i(e);
if (r === "array") {
    for (n in e) {
        if (e.hasOwnProperty(n)) {
            s.call(t, e[n])
        }
    }
}
return t
}
6: 3
}

output is {4: 2, 2: 6, 6:3}

Answer 1

I don't think there's a direct solution in one step and of course it's not just a sort (a sort doesn't remove elements). A way to do this would be to build an intermediary map of objects to store the counts :

var allTypesArray = ["4", "4","2", "2", "2", "6", "2", "6", "6"];
var s = allTypesArray.reduce(function(m,v){
  m[v] = (m[v]||0)+1; return m;
}, {}); // builds {2: 4, 4: 2, 6: 3} 
var a = [];
for (k in s) a.push({k:k,n:s[k]});
// now we have [{"k":"2","n":4},{"k":"4","n":2},{"k":"6","n":3}] 
a.sort(function(a,b){ return b.n-a.n });
a = a.map(function(a) { return a.k });

Note that you don't need jQuery here. When you don't manipulate the DOM, you rarely need it.

Answer 2

Just adding my idea as well (a bit too late)

var allTypesArray = ["4", "4", "2", "2", "2", "6", "2", "6", "6"];
var map = allTypesArray.reduce(function(p, c) {
  p[c] = (p[c] || 0) + 1;
  return p;
}, {});

var newTypesArray = Object.keys(map).sort(function(a, b) {
  return map[b] - map[a];
});

console.log(newTypesArray)

Answer 3

I don't think jquery is needed here.

There are several great answers to this question already, but I have found reliability to be an issue in some browsers (namely Safari 10 -- though there could be others).

A somewhat ugly, but seemingly reliable, way to solve this is as follows:

function uniqueCountPreserve(inputArray){
    //Sorts the input array by the number of time
    //each element appears (largest to smallest)

    //Count the number of times each item
    //in the array occurs and save the counts to an object
    var arrayItemCounts = {};
    for (var i in inputArray){
        if (!(arrayItemCounts.hasOwnProperty(inputArray[i]))){
            arrayItemCounts[inputArray[i]] = 1
        } else {
            arrayItemCounts[inputArray[i]] += 1
        }
    }

    //Sort the keys by value (smallest to largest)
    //please see Markus R's answer at: http://stackoverflow.com/a/16794116/4898004
    var keysByCount = Object.keys(arrayItemCounts).sort(function(a, b){
        return arrayItemCounts[a]-arrayItemCounts[b];
    });

    //Reverse the Array and Return
    return(keysByCount.reverse())
}

---

Test

uniqueCountPreserve(allTypesArray)
//["2", "6", "4"]