Remove Duplicates The Shortest Way

#javascript #webdev #array

function removeDuplicate(arr) {
  return [...new Set(arr)]
}

Remove duplicates from an array in javascript the shortest way.👍Using Set object where it only contains unique values (remove repeated ones). Then with spread operator spreads the values into an array again. 😎

Entfernen Sie Duplikate auf kürzestem Weg aus einem Array in #Javascript. Dann spreizt der Operator mit spread die Werte wieder in ein Array.

Top comments (7)

vatsal-uppal-1997 • Jan 25 '20

If you don't want to use Sets (because reasons). This might be the shortest:

function removeDuplicates(arr) {
    return Object.keys(arr.reduce((acc, val) => {
        acc[val] = val
        return acc
    }, { })).map(val => Number(val))
}

Jingles (Hong Jing) • Jan 26 '20

Does this method keep it's ordering, all the time?

Pacharapol Withayasakpunt • Jan 26 '20 • Edited

No, Object.keys(arr.reduce((acc, val) => { acc[val] = val return acc }, { })) is essentially Object.fromEntries(arr.map((val) => [val, val])). So, it is essentially the same method as Set

I would argue that the classical way might be as short, while keeping order, not sure about performance, though.

function removeDuplicates(arr) {
    return arr.filter((a, i) => arr.indexOf(a) === i)
}

Actually, the third argument of filter callback is arr as well, so you can .filter((v,i,a)=>a.indexOf(v)==i)

Array.prototype.distinct = function () { return this.filter((v, i, a) => a.indexOf(v) == i) }

Brian • Feb 2 '20 • Edited

Just to note that Set values are compared by reference for uniqueness - this can catch you out if your Array contains objects rather than primitive types

Islam Sayed • Feb 2 '20

Great advice! But how can we consider objects as duplicates even if they have same properties when they are passed by reference. So I think objects case is not applicable to this problem.

Brian • Feb 3 '20 • Edited

If you considered these objects duplicates [{id:1}, {id:1}], the Set approach won't suit. In this case though you'd probably need to use a utility library like Lodash: _.uniqWith(objects, _.isEqual)