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Remove Duplicates The Shortest Way

Islam Sayed on January 25, 2020

function removeDuplicate(arr) { return [ Set(arr)] } Remove duplicates from an array in javascript the shortest way.👍Using Set object w... [Read Full]
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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))

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


No, Object.keys(arr.reduce((acc, val) => { acc[val] = val return acc }, { })) is essentially Object.fromEntries( => [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) }

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


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.


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)

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