javascriptarrayscollectionssyntaxecmascript-harmony

Reputation: 21517

How to convert Set to Array?

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 ?

Upvotes: 950

Answers (11)

Darren Evans

Reputation: 741

As a web dev newcomer, I've been experimenting with Sets.

mySet = new Set([1, 2, 3, 4, 5]);

Create an array from values in a Set:

const myArray = [...mySet];

Transform values in a Set using map method to an array:

const myArray = [...mySet].map((x) => x * 2);

After transforming with map method, maybe you want to store them back in a Set to use the newer Set instance methods like intersection() or difference() etc:

const transformedSet = new Set([...mySet].map((x) => x * 2));

Here's an example of transforming the values of a Set of objects instead of a simple array of numbers:

mySet = new Set([
    { name: "John", age: 22 },
    { name: "Jane", age: 25 },
]);

const transformedSet = new Set(
    [...mySet].map((x) => ({ ...x, name: x.name.toUpperCase() })),
);

Upvotes: 0

adeneo

Reputation: 318332

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));

Upvotes: 1608

Dmitriy Malayev

Reputation: 81

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

}

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

Upvotes: -2

Drashti Trivedi

Reputation: 31

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]);

Upvotes: 0

Ekram Mallick

Reputation: 31

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);

Upvotes: 1

zdrsoft

Reputation: 2607

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.

Upvotes: -1

Alireza

Reputation: 104870

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));

Upvotes: 0

Roland

Reputation: 9721

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)

Upvotes: 12

d0wn

Reputation: 171

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.

Upvotes: 0