Search for documents with similar arrays in MongoDB and order by similarity value

Let us create a collection with documents −

> db.demo123.insertOne({"ListOfSubject":['MySQL', 'MongoDB', 'Java']}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f24ac140daf4c2a3544b8") } > db.demo123.insertOne({"ListOfSubject":['Python', 'MongoDB', 'C']}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f24cd140daf4c2a3544b9") } > db.demo123.insertOne({"ListOfSubject":['MySQL', 'MongoDB', 'C++']}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f24ce140daf4c2a3544ba") }

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

> db.demo123.find();

This will produce the following output −

{ "_id" : ObjectId("5e2f24ac140daf4c2a3544b8"), "ListOfSubject" : [ "MySQL", "MongoDB", "Java" ] } { "_id" : ObjectId("5e2f24cd140daf4c2a3544b9"), "ListOfSubject" : [ "Python", "MongoDB", "C" ] } { "_id" : ObjectId("5e2f24ce140daf4c2a3544ba"), "ListOfSubject" : [ "MySQL", "MongoDB", "C++" ] }

Following is the query to search for document with similar arrays and order them −

> var subjects = ['MySQL', 'MongoDB', 'Java']; > db.demo123.aggregate([ ...    {$unwind: "$ListOfSubject"}, ...    {$match: {ListOfSubject:{ $in:subjects}}}, ...    {$group: {_id: "$_id", number: {$sum: 1}}}, ...    {$project: {_id: 1, number: 1, percentage: {$divide: ["$number",subjects.length]}}}, ...    {$sort: {percentage: -1}} ... ]);

This will produce the following output −

{ "_id" : ObjectId("5e2f24ac140daf4c2a3544b8"), "number" : 3, "percentage" : 1 } { "_id" : ObjectId("5e2f24ce140daf4c2a3544ba"), "number" : 2, "percentage" : 0.6666666666666666 } { "_id" : ObjectId("5e2f24cd140daf4c2a3544b9"), "number" : 1, "percentage" : 0.3333333333333333 }