// to be executed on common.rateplans collection
db.rateplans.aggregate([
    {$match: {"hotel_id":1}},
    {$group: {
        "_id": {
            "room_type": "$room_type"
        },
        "cnt": {$sum: 1}
    }},
    {$project: {
        "_id": 0,
        "room_type": "$_id.room_type",
        "rp_count": "$cnt"
    }},
    {$sort: {
        "rp_count": -1
    }}
])