Removing array index reference when using json_encode()

You are ignoring the return value of array_values in your existing attempt to reindex the array. Correct is

$arr['dates'] = array_values($arr['dates']);

The reindexing should also be moved outside the foreach loop, there is no point in reindexing multiple times.

Use array_values() for your issue:

$arr['dates'] = array_values($arr['dates']);
//..
$arr = json_encode($arr);

Why? Because you're unsetting array's key without re-ordering it. So after this the only way to keep that in JSON will be encode keys too. After applying array_values(), however, you'll get ordered keys (starting from 0) which can be encoded properly without including keys.

In Laravel collections(just in case) you can do

    $newArray = $collection->values()->toArray();

or

    $jsonEncoded = $collection->values()->toJson();