$avg - Amazon DocumentDB
Example (MongoDB Shell)Code examples
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$avg

The $avg aggregation operator in Amazon DocumentDB calculates the average value of the specified expression across the documents that are input to the stage. This operator is useful for computing the average of a numeric field or expression across a set of documents.

Parameters

  • expression: The expression to use to calculate the average. This can be a field path (e.g. "$field") or an expression (e.g. { $multiply: ["$field1", "$field2"] }).

Example (MongoDB Shell)

The following example demonstrates how to use the $avg operator to calculate the average score across a set of student documents.

Create sample documents

db.students.insertMany([
  { name: "John", score: 85 },
  { name: "Jane", score: 92 },
  { name: "Bob", score: 78 },
  { name: "Alice", score: 90 }
]);

Query example

db.students.aggregate([
  { $group: { 
    _id: null,
    avgScore: { $avg: "$score" }
  }}
]);

Output

[
  {
    "_id": null,
    "avgScore": 86.25
  }
]

Code examples

To view a code example for using the $avg command, choose the tab for the language that you want to use:

Node.js
const { MongoClient } = require('mongodb');

async function calculateAvgScore() {
  const client = await MongoClient.connect('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  const db = client.db('test');
  const result = await db.collection('students').aggregate([
    { $group: {
      _id: null,
      avgScore: { $avg: '$score' }
    }}
  ]).toArray();
  console.log(result);
  await client.close();
}

calculateAvgScore();
Python
from pymongo import MongoClient

def calculate_avg_score():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    db = client.test
    result = list(db.students.aggregate([
        { '$group': {
            '_id': None,
            'avgScore': { '$avg': '$score' }
        }}
    ]))
    print(result)
    client.close()

calculate_avg_score()