$following_pipe[] = [
'$group' => ['_id' => '$' . $groupBy,
'org_data.center' => [
['$first' => '$org_data.center.longitude'],
['$first' => '$org_data.center.latitude'],
],
'org_data._id' => [
['$first' => '$_id'],
]
]
];
the group aggregate field 'center' must be defined as an expression inside an object