feedback option stats

db.feedbacks.aggregate([
    {$match : {
                "collection": "tests",
                "docId": {$in : [ObjectId("56c6dc8a995a2d6dc85f45eb") , ObjectId("5abcaf934e04790c26cad289"), ObjectId("56c6de2b995a2d6dc85f4828")]}
                }
    },
    {$unwind : "$mo"},
    {
        $lookup : {
            from : "feedback_options",
            localField: "mo",
            foreignField: "_id",
            as : "option_details"
        }
    },
    {$project : {
        "mo": 1,
        "option_details": {$arrayElemAt: ["$option_details", 0]},
        "rating": 1
        }
    },
    {$match : {"rating": {$in : [1, 2, 3, 4,5]}}},
    {$group :
            {
                _id: "$mo",
               count : {$sum : 1},
               optionText : {$first : "$option_details.text"},
               ratings : {$addToSet : "$rating"}
            }
    }
])