Mongo Group and sum with two fields

Question

I have documents like:

{
   \"from\":\"abc@sss.ffffd\",
   \"to\" :\"ssd@dff.dff\",
   \"email\": \"Hi hello\"
}

How can we calculate count o

Answer 1

Since you need to calculate number of emails exchanged between 2 addresses, it would be fair to project a unified between field as following:

db.a.aggregate([
    { $match: {
        to: { $exists: true },
        from: { $exists: true },
        email: { $exists: true }
    }}, 
    { $project: {
        between: { $cond: { 
            if: { $lte: [ { $strcasecmp: [ "$to", "$from" ] }, 0 ] }, 
            then: [ { $toLower: "$to" }, { $toLower: "$from" } ], 
            else: [ { $toLower: "$from" }, { $toLower: "$to" } ] }
        } 
    }},
    { $group: {
         "_id": "$between",
         "count": { $sum: 1 } 
    }},
    { $sort :{ count: -1 } }
])

Unification logic should be quite clear from the example: it is an alphabetically sorted array of both emails. The $match and $toLower parts are optional if you trust your data.

Documentation for operators used in the example:

• $match
• $exists
• $project
• $cond
• $lte
• $strcasecmp
• $toLower
• $group
• $sum
• $sort