M101JS-Exam-q2.js

db.messages.aggregate([
    {"$unwind":"$headers.To"},
    {$group: 
        {
            _id: '$_id',
            from: {$first: "$headers.From"},
            uniqueTo: {$addToSet: '$headers.To'}
        }
    },
    {"$unwind":"$uniqueTo"},
    {$group :
        { 
            _id : { From: "$from", To: '$uniqueTo' },
            count : {$sum : 1 }
        }     
     },
    {$sort: {"count":-1}},
    {$limit: 10}
])