Chunky Monkey code understanding

1

Hey everyone I need some clarification and help understanding.

I have completed this challange but I would really like more help understanding it. Please don’t flame me to much for breaking this down as much as I am about to.

This was my original code for “Chunky Monkey”

function chunkArrayInGroups(arr, size) {
  var newArray = [];
  for (var i = 0, a= 0; i < arr.length; i++) {
    newArray.push(arr.slice(a , size));    
    a += size;
    size += size;
  }
  return newArray; 
}
chunkArrayInGroups([0, 1, 2, 3, 4, 5], 2);

This returns this result: [[0,1][2,3][]]

I cannot understand why it did not return something else. In my head the code is saying this: step by step;

  1. We have a function.
  2. Hey I have an var which is ‘newArray’ and it equals ‘[]’
  3. Hey I have another var which is ‘loops’ and it equals ‘arr.length / size’
  4. Alright we are gonna do this ‘for’ loop.
  5. newArray now = newArray.push(arr.slice(0, 2));
    a. newArray = newArray.push([0,1])
    b. newArray = [[0,1]]
  6. newArray now = newArray.push(arr.slice(2, 4));
    a. newArray = newArray.push([2,3])
    b. newArray = [[0,1],[2,3]]
  7. newArray = newArray.push(arr.slice(4,6));
    a. newArray = newArray.push([4,5]);
    b. newArray = [[0,1],[2,3],[4,5]]
  8. Alright im done with ‘for’ loop here s ‘newArray’ like you asked.

I don’t understand why it is not returning the last array as [4,5] and adding that to the end of the array it had before. Instead it returns []… I don’t get it at all.

Now this is the code that works, and I get it fully.

> function chunkArrayInGroups(arr, size) {
>   var newArray = [];
>   for (var i = 0; i < arr.length; i += size) {
>     newArray.push(arr.slice(i , i + size));     
>   }
>   return newArray; 
> }
> chunkArrayInGroups([0, 1, 2, 3, 4, 5], 2);

Returns: [[0,1],[2,3],[4,5]]

So except for the fact that the working code looks cleaner then my original, I really don’t see why it would return a different outcome.

Thank you in advance for the help and clarification.

1 Like
2

Haiiiiyo.

You are just missing one tiny detail—the problem is this:

size += size

Which means that instead of slicing arrays of a fixed length (in this case 2), you are slicing increasingly larger intervals. If you log a and size, you will see something like this:

console.log(a, size) // First loop returns 0 2
console.log(a, size) // Second loop returns 2 4
console.log(a, size) // Third loop returns 6 8
// ... etc.

For this reason, you only get the results that you expect in the first two and then empty arrays for the rest of the loops.

I hope that helps. :slight_smile:

3

OMG Thank you so much. I 100% get it now. I don’t know why I didn’t catch that sooner. Finally I can get this problem off my mind and move onto the next one.

4

Out of curiosity, what is the “loops” variable for? It doesn’t look like you ever use it.

5

Haha I forgot I left that in. At first it was going to be a way for me to tell it how many loops for loops I wanted it to do, but then I noticed that it was pointless and I could do it a different way using “arr.length”. I meant to take it out before I posted this, but I guess I didn’t.

Thanks for pointing it out though, ill go edit it, so no one else thinks I’m to crazy.