$cursor=$collection_discussion->aggregate([
                    [ '$match' => ['_id' => $discussion_id]],
                    [
                        '$project' => [
                            'comments'=> [
                                '$filter' => [
                                    'input'=> '$comments',
                                    'as'=> 'comment',
                                    'cond' => [ '$eq' => [ '$$comment.group_id',$group_id ] ]
                                ]
                            ]
                        ]
                    ],[
                        '$project' => [
                            'comments'=> [
                                '$slice' => [
                                    [
                                        '$slice' => [
                                            '$comments',
                                            [
                                                '$subtract' => [ [ '$size' => [ '$comments' ] ], $list_count ]
                                            ]
                                        ]
                                    ], $lastRecordsLimit
                                ]
                            ]
                        ]
                    ]
                ]);