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

New from version 8.0.1.

The $trunc operator in Amazon DocumentDB truncates a number to a specified decimal place, removing digits without rounding.

Parameters

  • number: An expression that resolves to a number.

  • place: Optional. An integer expression between -20 and 100 that specifies the number of decimal places to truncate to. A negative value truncates to the left of the decimal. Defaults to 0.

Example (MongoDB Shell)

The following example shows how to use the $trunc operator to truncate numeric values to one decimal place.

Truncating with a positive place value

db.measurements.insertMany([
  {_id: 1, value: 3.456},
  {_id: 2, value: 7.891},
  {_id: 3, value: 12.345}
]);

Query example

db.measurements.aggregate([
  { $project: { truncated: { $trunc: ["$value", 1] } } }
]);

Output

[
  {_id: 1, truncated: 3.4},
  {_id: 2, truncated: 7.8},
  {_id: 3, truncated: 12.3}
]

Truncating with a negative place value

When place is negative, $trunc replaces digits to the left of the decimal with zeros. The following example truncates values using the first digit to the left of the decimal.

db.samples.insertMany([
  {_id: 1, value: 19.25},
  {_id: 2, value: 28.73},
  {_id: 3, value: 34.32}
]);
db.samples.aggregate([
  { $project: { truncated: { $trunc: ["$value", -1] } } }
]);

Output

[
  {_id: 1, truncated: 10},
  {_id: 2, truncated: 20},
  {_id: 3, truncated: 30}
]

Code examples

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

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

async function example() {
  const client = new MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false');
  try {
    await client.connect();
    const db = client.db('test');
    const collection = db.collection('measurements');
    const result = await collection.aggregate([
      { $project: { truncated: { $trunc: ["$value", 1] } } }
    ]).toArray();
    console.log(result);
  } finally {
    await client.close();
  }
}
example();
Python
from pymongo import MongoClient

def example():
    client = MongoClient('mongodb://<username>:<password>@<cluster-endpoint>:27017/?tls=true&tlsCAFile=global-bundle.pem&replicaSet=rs0&readPreference=secondaryPreferred&retryWrites=false')
    try:
        db = client['test']
        collection = db['measurements']
        result = list(collection.aggregate([
            {'$project': {'truncated': {'$trunc': ['$value', 1]}}}
        ]))
        print(result)
    finally:
        client.close()

example()