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Group with multiple fields and get the count of duplicate field values grouped together 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 }
Updated on: 14-May-2020
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