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Remove duplicates from an Array the short & sweet way!

Ajmal Hassan on November 22, 2019

tldr; const numbers = [1,2,2,3,3,3,4,4,4,4] console.log([...new Set(numbers)]) //output: [1,2,3,4] // OR console.log(Array.from(new ...

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Garet McKinley • Nov 22 '19

I'd be curious to see performance comparisons for this vs traditional deduping, like Array.filter(). The two way conversion feels like an expensive operation, but I have no basis for that other than the feeling.

Ajmal Hassan • Nov 22 '19

Infact, Array.filter() is more performant but it's a bit harder to understand it's working when compared to this.

array.filter((item, index)=> array.indexOf(item)===index)

If performance isn't critical then the method in the post is more readable and simpler.

Leonardo Santos • Mar 6 '20

I don't think the Array.filter + Array.indexOf approach is more performant. Unless I'm missing something.

Both are linear, so for every item you are filtering, you are also iterating over the array again to find an index. Therefore, in the worst case, it will end up having a quadratic O(n^2) performance, which is really bad.

Garet McKinley • Nov 24 '19

Maybe it's just my own ignorance not being familiar with the Set syntax. But the Array.filter method is so widely used that I'd know instantly what that line did. The example in the original post would confuse me to no end if there were no comments. I'd definitely have to google to figure out what's going on and why.

I'm sure the syntax is nice when you're familiar with it, but it's just not something that's done very often, so I'd definitely always leave a comment before it if you're using it in a code base that other people will have to read eventually.

Ajmal Hassan • Nov 24 '19

I agree, Set isn't something we commonly use.

Ankit kumar shukla • Nov 22 '19

is this work with like array data [{id=1,name='a'},{id=1,name='b'},{id=2,name='c'},{id=3,name='d'},{id=2,name='e'},{id=3,name='f'},{id=4,name='ag'},{id=5,name='au'}]

Ajmal Hassan • Nov 22 '19

No, it won't.

The above method only works for Primitive Types (number, string, boolean, null, undefined) in the array.

so,

const primitivesArr = [true, false, true, false, undefined, 1, undefined, 'hello', 1, 'hello']

console.log([...new Set(primitivesArr)])
// output: [true, false, undefined, 1, "hello"]