CODEWITHSUNDEEP
javascript
sir-haver
sir-haver

Reputation: 3592

Return undefined on empty nested arrays with flat

I'm using flat() to count the number of empty or undefined items inside a nested array.

[[undefined, 4], [4]]

Using flat on this array will return 3 items:

  1. undefined
  2. 4
  3. 4

However on this array:

[[], [], []]

using flat will return an empty array.

Is there a way to use it so it returns 3 undefined items?

Upvotes: 2

Views: 335

Answers (3)

Rajneesh
Rajneesh

Reputation: 5308

If your array is n-level nested then you can create recursive function to achieve the desired result:

const flat = arr => arr.flatMap(o=> o?.length ? flat(o) : Array.isArray(o) ? undefined : o );

console.log(flat([[], [], []]));
console.log(flat([[undefined, 4], [4]]));
console.log(flat([[undefined, [[],[],[]], 4], [4,[]]]));

Upvotes: 0

YJR
YJR

Reputation: 1202

arr=[[],[],[]]

console.log(arr.reduce((acc, val) => acc.concat(val==''?undefined:val),[]));

according to js MDN docs combination of reducer and concat simmilar to the exact Array.prototype.flat function. therefor altering it you can get your expected answer.the code for that is as above.

Upvotes: 1

Anton Marinenko
Anton Marinenko

Reputation: 2982

You have to use flatMap for this reason:

[[], [], []].flatMap(item => item.length ? item : undefined)

returns what you need

Upvotes: 5

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