Return PHP object by index number (not name)

Goal: retrieve an element of data from within a PHP object by number.

This is the print_r($data) of the object:

stdClass Object
(
    [0] => stdClass Object
        (
            [TheKey] => 1456
            [ThingName] => Malibu
            [ThingID] => 7037
            [MemberOf] => California
            [ListID] => 7035
            [UserID] => 157
            [UserName] => John Doe
        )
)

I can't figure out how to pull a value out of it. This is only one record of a multi-record object that should be by id rather than a name.

These are some failed attempts to illustrate what the goal is:

echo $data -> 0 -> UserName;
echo $data[0] -> UserName;