I need to change the format of an array returned in CodeIgniter, leaving a field of the database as index, I made the same querys in PHP and CodeIgniter and both are different, any suggestions? I am using result_array () in CodeIgniter and also result ();

I need this:

Array
(
    [1_1] => Array
        (
            [0] => 1_1
            [1] => 16
            [2] => ch
            [3] => Chemistry
        )

    [1_2] => Array
        (
            [0] => 1_2
            [1] => 17
            [2] => ch
            [3] => Chemistry
        )

    [2_3] => Array
        (
            [0] => 2_3
            [1] => 18
            [2] => ch
            [3] => Chemistry
        )

    [2_5] => Array
        (
            [0] => 2_5
            [1] => 19
            [2] => ch
            [3] => Chemistry
        )

    [9_1] => Array
        (
            [0] => 9_1
            [1] => 20
            [2] => ch
            [3] => Chemistry
        )

)

Query results:

Array
(
    [0] => Array
        (
            [pos] => 1_1
            [tbl_id] => 16
            [sub_id] => ch
            [sub_name] => Chemistry
        )

    [1] => Array
        (
            [pos] => 1_2
            [tbl_id] => 17
            [sub_id] => ch
            [sub_name] => Chemistry
        )

    [2] => Array
        (
            [pos] => 2_3
            [tbl_id] => 18
            [sub_id] => ch
            [sub_name] => Chemistry
        )

    [3] => Array
        (
            [pos] => 2_5
            [tbl_id] => 19
            [sub_id] => ch
            [sub_name] => Chemistry
        )

    [4] => Array
        (
            [pos] => 9_1
            [tbl_id] => 20
            [sub_id] => ch
            [sub_name] => Chemistry
        )

)

How can I delete the array that is at the beginning? Thank you.