How to perform intersection of sets between the documents in a single collection in MongoDB?

You can use $setIntersection for this. Let us first create a collection with documents −

> db.setInterSectionDemo.insertOne(
...    {"_id":101, "Value1":[55,67,89]}
... );
{ "acknowledged" : true, "insertedId" : 101 }
> db.setInterSectionDemo.insertOne(
...    {"_id":102, "Value2":[90,45,55]}
... );
{ "acknowledged" : true, "insertedId" : 102 }
> db.setInterSectionDemo.insertOne(
...    {"_id":103, "Value3":[92,67,45]}
... );
{ "acknowledged" : true, "insertedId" : 103 }

Following is the query to display all documents from a collection with the help of find() method −

> db.setInterSectionDemo.find().pretty();

This will produce the following output −

{ "_id" : 101, "Value1" : [ 55, 67, 89 ] }
{ "_id" : 102, "Value2" : [ 90, 45, 55 ] }
{ "_id" : 103, "Value3" : [ 92, 67, 45 ]

Here is the query to find intersection of sets between the documents in a single collection in MongoDB −

> db.setInterSectionDemo.aggregate([
...    {
...       "$match": {
...          "_id": { "$in": [101, 103] }
...       }
...    },
...    {
...       "$group": {
...          "_id": 0,
...          "firstValue": { "$first": "$Value1" },
...          "secondValue": { "$last": "$Value3" }
...       }
...    },
...    {
...       "$project": {
...          "firstValue": 1,
...          "secondValue": 1,
...          "CommonValue": { "$setIntersection": [ "$firstValue", "$secondValue" ] },
...          "_id": 0
...       }
...    }
... ]);

This will produce the following output −

{ "firstValue" : [ 55, 67, 89 ], "secondValue" : [ 92, 67, 45 ], "CommonValue" : [ 67 ] }