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How to count number of distinct values per field/ key in MongoDB?
You can use the distinct command for this. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −
> db.distinctCountValuesDemo.insertOne({"StudentFirstName":"John","StudentFavouriteSubject":["C","C++","Java","MySQL","C","C++"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8a39f193b406bd3df60e07")
}
> db.distinctCountValuesDemo.insertOne({"StudentFirstName":"Larry","StudentFavouriteSubject":["MongoDB","SQL Server"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c8a3a1193b406bd3df60e08")
}Display all documents from a collection with the help of find() method. The query is as follows −
> db.distinctCountValuesDemo.find().pretty();
The following is the output −
{
"_id" : ObjectId("5c8a39f193b406bd3df60e07"),
"StudentFirstName" : "John",
"StudentFavouriteSubject" : [
"C",
"C++",
"Java",
"MySQL",
"C",
"C++"
]
}
{
"_id" : ObjectId("5c8a3a1193b406bd3df60e08"),
"StudentFirstName" : "Larry",
"StudentFavouriteSubject" : [
"MongoDB",
"SQL Server"
]
}Here is the query to find a number of distinct values per field/key −
> db.distinctCountValuesDemo.distinct('StudentFavouriteSubject');The following is the output −
[ "C", "C++", "Java", "MySQL", "MongoDB", "SQL Server" ]
Here is the query to find the length of the distinct value in the array −
> db.distinctCountValuesDemo.distinct('StudentFavouriteSubject').length;The following is the output −
6
Updated on: 30-Jul-2019
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