How to convert Set to Array?

Question

Set seems like a nice way to create Arrays with guaranteed unique elements, but it does not expose any good way to get properties, except for generator [Set].values, which is called in an awkward way of mySet.values.next().

This would have been ok, if you could call map and similar functions on Sets. But you cannot do that, as well.

I've tried Array.from, but seems to be converting only array-like (NodeList and TypedArrays ?) objects to Array. Another try: Object.keys does not work for Sets, and Set.prototype does not have similar static method.

So, the question: Is there any convenient inbuilt method for creating an Array with values of a given Set ? (Order of element does not really matter).

if no such option exists, then maybe there is a nice idiomatic one-liner for doing that ? like, using for...of, or similar ?

Answer 1

if no such option exists, then maybe there is a nice idiomatic one-liner for doing that ? like, using for...of, or similar ?

Indeed, there are several ways to convert a Set to an Array:

• Using Array.from:

Note: safer for TypeScript.

const array = Array.from(mySet);

• Simply spreading the Set out in an array:

Note: Spreading a Set has issues when compiled with TypeScript (See issue #8856). It's safer to use Array.from above instead.

const array = [...mySet];

• The old-fashioned way, iterating and pushing to a new array (Sets do have forEach):

const array = [];
mySet.forEach(v => array.push(v));

• Previously, using the non-standard, and now deprecated array comprehension syntax:

const array = [v for (v of mySet)];

Answer 2

via https://speakerdeck.com/anguscroll/es6-uncensored by Angus Croll

It turns out, we can use spread operator:

var myArr = [...mySet];

Or, alternatively, use Array.from:

var myArr = Array.from(mySet);

Answer 3

Assuming you are just using Set temporarily to get unique values in an array and then converting back to an Array, try using this:

_.uniq([])

This relies on using underscore or lo-dash.

Answer 4

Perhaps to late to the party, but you could just do the following:

const set = new Set(['a', 'b']);
const values = set.values();
const array = Array.from(values);

This should work without problems in browsers that have support for ES6 or if you have a shim that correctly polyfills the above functionality.

Edit: Today you can just use what @c69 suggests:

const set = new Set(['a', 'b']);
const array = [...set]; // or Array.from(set)

Answer 5

The code below creates a set from an array and then, using the ... operator.

var arr=[1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9,];
var set=new Set(arr);
let setarr=[...set];
console.log(setarr);

Answer 6

In my case the solution was:

var testSet = new Set();
var testArray = [];

testSet.add("1");
testSet.add("2");
testSet.add("2"); // duplicate item
testSet.add("3");

var someFunction = function (value1, value2, setItself) {
    testArray.push(value1);
};

testSet.forEach(someFunction);

console.log("testArray: " + testArray);

value1 equals value2 => The value contained in the the current position in the Set. The same value is passed for both arguments

Worked under IE11.

Answer 7

Using Set and converting it to an array is very similar to copying an Array...

So you can use the same methods for copying an array which is very easy in ES6

For example, you can use ...

Imagine you have this Set below:

const a = new Set(["Alireza", "Dezfoolian", "is", "a", "developer"]);

You can simply convert it using:

const b = [...a];

and the result is:

["Alireza", "Dezfoolian", "is", "a", "developer"]

An array and now you can use all methods that you can use for an array...

Other common ways of doing it:

const b = Array.from(a);

or using loops like:

const b = [];
a.forEach(v => b.push(v));

Answer 8

Here is an easy way to get only unique raw values from array. If you convert the array to Set and after this, do the conversion from Set to array. This conversion works only for raw values, for objects in the array it is not valid. Try it by yourself.

    let myObj1 = {
        name: "Dany",
        age: 35,
        address: "str. My street N5"
    }

    let myObj2 = {
        name: "Dany",
        age: 35,
        address: "str. My street N5"
    }

    var myArray = [55, 44, 65, myObj1, 44, myObj2, 15, 25, 65, 30];
    console.log(myArray);

    var mySet = new Set(myArray);
    console.log(mySet);

    console.log(mySet.size === myArray.length);// !! The size differs because Set has only unique items

    let uniqueArray = [...mySet];
    console.log(uniqueArray); 
    // Here you will see your new array have only unique elements with raw 
    // values. The objects are not filtered as unique values by Set.
    // Try it by yourself.

Answer 9

I would prefer to start with removing duplications from an array and then try to sort. Return the 1st element from new array.

    function processData(myArray) {
        var s = new Set(myArray);
        var arr = [...s];
        return arr.sort((a,b) => b-a)[1];
    }
    
    console.log(processData([2,3,6,6,5]);

Answer 10

function countUniqueValues(arr) {
  return Array.from(new Set(arr)).length 

}

console.log(countUniqueValues([1, 2, 3, 4, 4, 4, 7, 7, 12, 12, 13]))