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

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 2

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 3

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 4

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 5

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

let array = Array.from(mySet);

Simply spreading the Set out in an array

let array = [...mySet];

The old fashion way, iterating and pushing to a new array (Sets do have forEach)

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

Using a fancier for...of loop (this doesn't seem to work in Chrome anymore)

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

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.