Change the array KEY to a value from sub array

This may be a bit late but I've been looking for a solution to the same problem. But since all of the other answers involve loops and are too complicated imho, I've been trying some stuff myself.

The outcome

$items = array_combine(array_column($items, 'id'), $items);

It's as simple as that.

This won't do it in-place, but:

$new_plan = array();
foreach ($plan as $item)
{
  $new_plan[$item['id']] = $item;
}