Extracting last element of nested array with recursion

Question

I want to flat an array, recursion function calls itself till the last element array but not the last element string, I feel like I am missing something important in understanding how recursion works, the string itself is not added to an empty array.

const nested = [[[[[['string']]]]], 5, '7'];

const funcTest = function (arr) {
  const final = [];
  arr.forEach(el => {
    if (Array.isArray(el)) {
      console.log(el);
      funcTest(el);
    } else final.push(el);
  });
  return final;
};  

console.log(funcTest(nested));

Did you try .flat? Consider [[[[[['string']]]]], 5, '7'].flat(Infinity) — Wyck
– Wyck, Commented Nov 17, 2021 at 20:45

TAHER El Mehdi · Accepted Answer · 2021-11-17 20:57:26Z

2

You can Flattening all nested arrays With flat taking argument depth of Infinity:

    const nested = [[[[[["string"]]]]], 5, "7"];
    nested.flat(Infinity); //['string', 5, '7']

depth: The depth level specifying how deep a nested array structure should be flattened. Defaults to 1.

edited Nov 17, 2021 at 20:57

answered Nov 17, 2021 at 20:47

TAHER El Mehdi

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4 Comments

TAHER El Mehdi Over a year ago

Thanks for the clarification!

Nina Scholz Over a year ago

if that is really an answer to the recursive problem, the question would be a duplicate.

TAHER El Mehdi Over a year ago

It's not the answer, but just I would share a trick to flattening an array without using recursion or for-loops!

G-T Over a year ago

Thank you very much

Nina Scholz · Accepted Answer · 2021-11-17 20:50:20Z

0

You need to add the result of the recursive calls.

const
    nested = [[[[[['string']]]]], 5, '7'];

const funcTest = function (arr) {
  const final = [];
  arr.forEach(el => {
    if (Array.isArray(el)) {
      console.log(el);
      final.push(...funcTest(el)); // <-
    } else final.push(el);
  });
  return final;
};  

console.log(funcTest(nested));

Another recursive approach:

const
    nested = [[[[[['string']]]]], 5, '7'];
    flatValues = item => Array.isArray(item)
        ? item.flatMap(flatValues)
        : item;

console.log(flatValues(nested));

edited Nov 17, 2021 at 20:50

answered Nov 17, 2021 at 20:45

Nina Scholz

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Comments

Антон Невзгодов · Accepted Answer · 2021-11-17 20:51:09Z

0

The issue here is that you don't use the return value of the recursive funcTest call.

What you want to do:

const superFlat = (arr) => {
  const result = [];
  
  arr.forEach((item) => {
    if (!Array.isArray(item)) result.push(item);
    else result.push(...superFlat(item));
  });

  return result;
}

Or just use arr.flat(Infinity)

answered Nov 17, 2021 at 20:51

Антон Невзгодов

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1 Comment

G-T Over a year ago

Thank you very much

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