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How to remove duplicate values inside a list in MongoDB?
You can use aggregate framework along with $setUnion operator. Let us first create a collection with documents −
> db.removeDuplicatesDemo.insertOne({"InstructorName":"Chris","InstructorAge":34,"InstructorSubject":
["Java","C","Java","C++","MongoDB","MySQL","MongoDB"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cb9d96c895c4fd159f80807")
}Following is the query to display all documents from the collection with the help of find() method −
> db.removeDuplicatesDemo.find().pretty();
This will produce the following output −
{
"_id" : ObjectId("5cb9d96c895c4fd159f80807"),
"InstructorName" : "Chris",
"InstructorAge" : 34,
"InstructorSubject" : [
"Java",
"C",
"Java",
"C++",
"MongoDB",
"MySQL",
"MongoDB"
]
}Following is the query to remove duplicate values inside a list in MongoDB −
> db.removeDuplicatesDemo.aggregate([
... { "$project": {
... "InstructorName":1,
... "InstructorAge" :1,
... "InstructorSubject" :{ "$setUnion": [ "$InstructorSubject", [] ] }
... }}
... ]).pretty();This will produce the following output −
{
"_id" : ObjectId("5cb9d96c895c4fd159f80807"),
"InstructorName" : "Chris",
"InstructorAge" : 34,
"InstructorSubject" : [
"C",
"C++",
"Java",
"MongoDB",
"MySQL"
]
}
Updated on: 30-Jul-2019
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