How to group_by in mongoDb with the output results?

Below is my code..

 group = {
    $group: { 
        "_id": {
            "user_email": "$user_email",
            "sender_email": "$sender_email"
        },
        "count": { "$sum": 1 }

    }
};  


Schema.aggregate(([group]),function(errors,results){

                  console.log(results);             
                  });

my output value is:

[ { _id: 
     { user_email: '123@gmail.com',
       sender_email: '235@gmail.com' },
    count: 5 },
  { _id: 
     { user_email: '123m@gmail.com',
       sender_email: '235@gmail.com' },
    count: 16 },
  { _id: 
     { user_email: '455@gmail.com',
       sender_email: '785@gmail.com' },
    count: 8 },
  { _id: 
     { user_email: '123@gmail.com',
       sender_email: '235@gmail.com' },
    count: 4 } ]

The above record shows the individual poke count.. i need to know that how many user_email has poked sender_email.(an user_email can poke a sender_email for many times but if the sender_email is poked for many times by a user_email i need not want the count as 'many' but i need the count as 1,in the same way if the various users have poked the sender_email i do not want the count of how many times each user has poked sender_email but how many user_email has poked sender_email). I need a mongoDb query for it?

{ user_email: '123@gmail.com',
       sender_email: '235@gmail.com' },
    count: 5 }

123@gmail.com poked 235@gmail.com for 5 times but i need to know the count of how many individual sender_email has been poked by various user_email without passing any parameter?

via Jagadeesh