Group with Multiple Fields and Count Duplicate Values in MongoDB

For this, use MongoDB aggregate and within that, use $cond. The $cond evaluates a boolean expression to return one of the two specified return expressions.

Let us first create a collection with documents −

> db.demo536.insertOne({"Name1":"Chris","Name2":"David"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e8c843eef4dcbee04fbbc01")
}
> db.demo536.insertOne({"Name1":"David","Name2":"Chris"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e8c843fef4dcbee04fbbc02")
}
> db.demo536.insertOne({"Name1":"Bob","Name2":"Sam"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e8c843fef4dcbee04fbbc03")
}
> db.demo536.insertOne({"Name1":"Chris","Name2":"David"});{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e8c843fef4dcbee04fbbc04")
}

Display all documents from a collection with the help of find() method −

> db.demo536.find();

This will produce the following output −

{ "_id" : ObjectId("5e8c843eef4dcbee04fbbc01"), "Name1" : "Chris", "Name2" : "David" }
{ "_id" : ObjectId("5e8c843fef4dcbee04fbbc02"), "Name1" : "David", "Name2" : "Chris" }
{ "_id" : ObjectId("5e8c843fef4dcbee04fbbc03"), "Name1" : "Bob", "Name2" : "Sam" }
{ "_id" : ObjectId("5e8c843fef4dcbee04fbbc04"), "Name1" : "Chris", "Name2" : "David" }

Following is the query to group with multiple fields −

> db.demo536.aggregate([
... {
...    $project:
...    {
...       FirstName1:
...       {
...          $cond: { if: { $gte: [ "$Name1", "$Name2" ] }, then: "$Name2", else: "$Name1" }
...       },
...       FirstName2:
...       {
...          $cond: { if: { $lt: [ "$Name1", "$Name2" ] }, then: "$Name2", else: "$Name1" }
...       }
...    }
... }
... ,{
...    $group:
...    {
...       _id:
...       {
...          Name1: "$FirstName1",
...          Name2: "$FirstName2"
...       }
...       ,count: { $sum: 1}
...    }
... }
... ])

This will produce the following output &imnus;

{ "_id" : { "Name1" : "Bob", "Name2" : "Sam" }, "count" : 1 }
{ "_id" : { "Name1" : "Chris", "Name2" : "David" }, "count" : 3 }