CODEWITHSUNDEEP
mongodbmongoosemongodb-query
axtscz
axtscz

Reputation: 691

Counting how many times unique values occur in an array across a MongoDB collection

So I have a collection of users. The user document is a very simple document, and looks like this: 

{
   username: "player101",
   badges: ["score10", "score100"]
}

So how can I query to see how many times each unique value in the badges array occurs across the entire collection?

Upvotes: 0

Views: 394

Answers (1)

Mr Tarsa
Mr Tarsa

Reputation: 6652

Use aggregation with $unwind and $group stages, where you can sum badges with $sum arithmetic operator

db.players.aggregate([ 
  { 
    $unwind: "$badges" 
  }, 
  { 
    $group: 
      { 
        _id: "$badges", 
        count: { $sum: 1 } 
      } 
  } 
]);

on collection players with documents

{ "username" : "player101", "badges" : [ "score10", "score100" ] }
{ "username" : "player102", "badges" : [ "score11", "score100" ] }
{ "username" : "player103", "badges" : [ "score11", "score101" ] }
{ "username" : "player104", "badges" : [ "score12", "score100" ] }

gives you the result

{ "_id" : "score101", "count" : 1 }
{ "_id" : "score11", "count" : 2 }
{ "_id" : "score12", "count" : 1 }
{ "_id" : "score100", "count" : 3 }
{ "_id" : "score10", "count" : 1 }

Upvotes: 1

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