# Getting unique values within two arrays in one MongoDB document

MongoDBDatabaseBig Data Analytics

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"
]
}
Published on 15-May-2020 11:31:01