Getting unique values within two arrays in one MongoDB document

To get unique values within two arrays in a document, use a $setUnion in aggregate(). The $setUnion takes two or more arrays and returns an array containing the elements that appear in any input array.

Let us create a collection with documents −

>db.demo608.insertOne({"ListOfName1":["John","Chris","Bob","David"],"ListOfName2":["Bob", "Sam","John","Robert","Chris"]} ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e974542f57d0dc0b182d62b") }

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

> db.demo608.find().pretty();

This will produce the following output −

{    "_id" : ObjectId("5e974542f57d0dc0b182d62b"),    "ListOfName1" : [       "John",       "Chris",       "Bob",       "David"    ],    "ListOfName2" : [       "Bob",       "Sam",       "John",       "Robert",       "Chris"    ] }

Following is the query to get unique values within two arrays in one MongoDB document −

> db.demo608.aggregate([ ...    {$project:{SetOfNames:{$setUnion:['$ListOfName1','$ListOfName2']}}} ... ]).pretty();

This will produce the following output −

{    "_id" : ObjectId("5e974542f57d0dc0b182d62b"),    "SetOfNames" : [       "Bob",       "Chris",       "David",       "John",       "Robert",       "Sam"    ] }