### nest

Given a flat array of objects linked to one another, it will nest them recursively.
Useful for nesting comments, such as the ones on reddit.com.

Use recursion. Use `Array.filter()` to filter the items where the `id` matches the `link`,
then use `Array.map()` to map each one to a new object that has a `children` property which
recursively nests the items based on which ones are children of the current item.

```js
const nest = (items, id = null, link = 'parent_id') =>
  items.filter(item => item[link] === id).map(item => ({ ...item, children: nest(items, item.id) }))
```

```js
// One top level comment
const comments = [
  { id: 1, parent_id: null },
  { id: 2, parent_id: 1 },
  { id: 3, parent_id: 1 },
  { id: 4, parent_id: 2 },
  { id: 5, parent_id: 4 }
]
const nestedComments = nest(comments) // [{ id: 1, parent_id: null, children: [...] }]
```