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Javascript – how to check how many [] symbols array contain

So, I have an array like this
const array=[1,2,3,4,[5,6],[[[[7,8]]]]]. I know that I can make it flat by flat function like this.
array.flat(4) // [1,2,3,4,5,6,7,8]

But as you know we can to this when we know array external count of this [] symbols. However we can fetch
any data that we don’t know how many [] this symbols are there in array. My question is that how to check
how many [] – this symbols are there within array.

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2

Answers


  1. 0

    You can flatten an array of unknown depth with

    array.flat(Infinity).length

    You can count elements yourself though with a loop and a stack without recursion (no maximum call stack size error), that would be more efficient since you don’t create a new array:

    console.log(countNestedArrayItems([1,2,3,4,[5,6],[[[[7,8]]]]]));

function countNestedArrayItems(arr) {

    let count = 0;
    const path = [];

    for (let i = 0; i < arr.length; i++) {

        const item = arr[i];

        if (Array.isArray(item)) {
            path.push(arr, i);
            i = -1;
            arr = item;
            continue;
        }

        count++;
        while(i === arr.length - 1 && path.length)  i = path.pop(), arr = path.pop();

    }

    return count;

}

    And a benchmark:

    ` Chrome/124
-----------------------------------------------------------------------------------
>              n=6       |       n=60        |       n=600       |      n=6000     
count    ■ 1.00x x1m 116 | ■ 1.00x x100k  94 | ■ 1.00x x100k 927 | ■ 1.00x x10k 860
flat()     1.75x x1m 203 |   2.17x x100k 204 |   2.29x  x10k 212 |   2.60x  x1k 224
-----------------------------------------------------------------------------------
https://github.com/silentmantra/benchmark `

    const $chunk = [1,2,3,4,[5,6],[[[[7,8,[1,2,3,4,[5,6],[[[[7,8]]]]]]]]]];
const $input = [];

function countNestedArrayItems(arr) {

    let count = 0;
    const path = [];

    for (let i = 0; i < arr.length; i++) {

        const item = arr[i];

        if (Array.isArray(item)) {
            path.push(arr, i);
            i = -1;
            arr = item;
            continue;
        }

        count++;
        while(i === arr.length - 1 && path.length)  i = path.pop(), arr = path.pop();

    }

    return count;

}
// @benchmark count
countNestedArrayItems($input);

// @benchmark flat()
$input.flat(Infinity).length;

/*@skip*/ fetch('https://cdn.jsdelivr.net/gh/silentmantra/benchmark/loader.js').then(r => r.text().then(eval));
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  2. 0

    Your question is not very clear, does this help?

    const array = [1, 2, 3, 4, [5, 6], [[[[7, 8]]]]];

function countNestedArrays(arr) {
  let count = 0;
  for (let i = 0; i < arr.length; i++) {
    if (Array.isArray(arr[i])) {
      count++;
      count += countNestedArrays(arr[i]);
    }
  }
  return count;
}

console.log(countNestedArrays(array));
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