Build A Tree Array From A Flat Array - Recursion

I got an assignment to display comments in a recursive way, something like so:

The data I got from the server was flat, meaning:
every item in the array holds a reference to its parent, like so:

const entries = [
  {
    index: 1,
    parent: 0
  },
  {
    index: 2,
    parent: 1
  },
  {
    index: 3,
    parent: 2
  },
   ...
   ...
   ];

After thinking how to "attack" this problem, I realized
If I want a recursive object, then the easiest solution is a recursive one

Here is the function that converts a flat array to a tree array:

const arrayToTree = (arr, parent = 0) =>
  arr.filter(item => item.parent === parent)
     .map(child => ({ ...child, children: arrayToTree(arr, 
     child.index) }));

A quick rundown:

• We first filter the root parent's children.
• Then we do the same to each of the children we just grabbed

My answer to the question on Stack overflow

Here is a codepen if you want to play more with the data ot the solution:

Sources that helped me:

• Styling Comment Threads