Flatten is slow about 30-seconds-of-code

[kirilloid]

Push returns length instead of just this

[kirilloid]

There are snippets already subjected to the same problem, e.g. Math.max(...arr)

[skatcat31]

This is a fair point. I hadn't looked at the flatten() snippet yet, but O(N^2) is usually reserved for very specific use cases(sorts, searches) and as such means that it should probably be addressed. Your provided snippet of

const flatten = arr => [].concat(...arr)

looks about right in terms of big O and avoids using any complicated memory tricks with comma operators. The only problem is it causes the stack to blow up. I'm not certain the alternate is better in terms of speed, but does reduce suffer from stack issues?

const flatten = arr => arr.reduce( ( a, v ) => Array.isArray( v ) ? a.concat( v ) : a.push( v ), [ ] )

uhh my flatten is failing for some reason... I'll look more into on lunch

[kirilloid]

Unfortunately there’s no concise, fast and large arrays-tolerant solution for that problem.
It’s either slow, or can blow up or is big and clumsy

[skatcat31]

As it stands simple modifications to that one keep breaking, and after looking at it closer I'm not certain it avoids the big O problem either if it did work as expected. If someone can find a good balance between O(N) and speed in a working function that doesn't explode we might want to adopt that, but otherwise this one is pretty smart and could still work. Just the issue should be mentioned.

[Chalarangelo]

Pretty much any array method that works through 100k elements will break down, so we can't do a lot about it, except eventually add a disclaimer. (There will be a separate issue to discuss this as a general guideline). I'm closing this issue for now, as we can't really do a lot about this, apart from accept that JS has its quirks.

[kirilloid]

So here's a (seemingly) fast, robust, but not beatiful solution.

const chunkedEach = (arr, fn, size = 10000) => {
  for (let i = 0; i < arr.length / size; i++) {
    fn(arr.slice(i * size, (i + 1) * size));
  }
};
const flatten = arr => {
  const result = [];
  arr.forEach(a => {
    if (Array.isArray(a)) {
      chunkedEach(a, sub => result.push(...sub));
    } else {
      result.push(a);
    }
  });
  return result;
);

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for any follow-up tasks.