How do I fill a new array with n distinct empty arrays, in a concise one-line initialization statement? [duplicate]

Question

Here is where I am stuck. I want to take this statement and revise it in a manner that the empty array I fill (which I surmise might not work with dynamic values), will initialize bucket to the n distinct empty arrays.

How do I do this? Is there a way to make this fill method behave in the intended manner?

let radix = 10;
let badBucket = [...Array(radix).fill([])];
let goodBucket = JSON.parse(JSON.stringify([...Array(radix).fill([])]));
badBucket[3].push(33);
goodBucket[3].push(33);
console.log(JSON.stringify(badBucket));
console.log(JSON.stringify(goodBucket));

If I were to push an item to bucket[0] like so bucket[0].push(1), the array contents would all have 1 [[10],[10],[10],[10],[10],[10],[10],[10]], which pretty much be undesireable — Vahe
– Vahe, Commented Sep 19, 2021 at 17:11
Is this one of those scenarios where If fill can accept a callback, I can return a new empty array from the callback, like so... fill(() => []) fingers crossed...awww, unfortunately that was not the case as hoped — Vahe
– Vahe, Commented Sep 19, 2021 at 17:13
const length = 10, bucket = Array.from({ length }).map(() => []); — Peter Seliger
– Peter Seliger, Commented Sep 19, 2021 at 17:21
@VaheJabagchourian ... It's not about one-liners or being this kind of extra smart . A practical solution very often is just a good enough balanced compromise in between a straightforward as possible but still readable / maintainable implementation. — Peter Seliger
– Peter Seliger, Commented Sep 19, 2021 at 17:34

Unmitigated · Accepted Answer · 2021-09-19 17:46:33Z

4

You can use the callback function of Array.from.

let length = 5;
let res = Array.from({length}, _=>[]);
console.log(res);

answered Sep 19, 2021 at 17:46

Unmitigated

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1 Comment

Vahe Over a year ago

Thank you for the specific alternate version using underscore object, this is quite desirable and produces a great readable response, with an object of 5 length that I can infer is assigned to an empty array.

Spectric · Accepted Answer · 2021-09-19 17:32:18Z

1

Try:

let radix = 10;
let bucket = [...Array(radix)].map(e=>[])
bucket[0].push(1)
console.log(JSON.stringify(bucket));

answered Sep 19, 2021 at 17:32

Spectric

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1 Comment

Vahe Over a year ago

This is exactly is the shortest length one liner that meets my desire. Thank you. Now I know which of the two functions (map ,fill) will accept the callback, and corresponding equivalent initialization stements.

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