PHP - Deleting an element of a JSON array changes the array syntax - php

Question

I can successfully delete elements of a JSON array with PHP, but I cannot understand why the JSON array changes syntax after deleting an element that's not the last one.
So, here's my User.json file:
[
{
"id": "kS79BhPx"
},
{
"id": "ycC7km7A"
},
{
"id": "hgF5D4es"
}
]
Here's my delete.php script:
$className = "Users";
// get the index
$index = (int)$_GET['index'];
//fetch data from json
$data = file_get_contents($className. '.json');
$data_array = json_decode($data, true);
// delete the row with the index
unset($data_array[$index]);
//encode back to json
$data = json_encode($data_array, JSON_PRETTY_PRINT);
file_put_contents($className. '.json', $data);
So, if I go to the following URL, just to test my php function:
https://example.com/delete.php?index=0
The script successfully deletes the first element of the JSON array, but then it changes into this:
{
"1": {
"id": "ycC7km7A"
},
"2": {
"id": "hgF5D4es"
}
}
Instead, if I set https://example.com/delete.php?index=2 - so I want to delete the last array's element - it saves it as follows:
[
{
"id": "kS79BhPx"
},
{
"id": "ycC7km7A"
}
]
This last result is what I need to achieve all the times I delete an element because I need the JSON array syntax to stay as [...], not as {...}.
What am I doing wrong in my PHP script?

Answer 1

Using unset() on an array (associative or not) in PHP will preserve the existing keys making the array associative. You need to reindex the array after using unset():
// delete the row with the index
unset($data_array[$index]);
$data_array = array_values($data_array);