MongoDB $round Operator

Posted in mongoDB Tutorial

Updated on Apr 08, 2024

By Mari Selvan

👁️ 13 - Views

⏳ 4 mins

💬 0

Photo Credit to CodeToFun

🙋 Introduction

Within MongoDB's aggregation framework, the $round operator offers a convenient way to round numerical values to a specified number of decimal places. This operator is particularly useful in scenarios where precision is required or when presenting data in a more concise format.

Let's delve into how the $round operator can be effectively utilized within MongoDB's aggregation pipelines.

💡 Syntax

The syntax for the $round method is straightforward:

syntax.js

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{ $round: { <expression>, <decimalPlaces> } }

$round: This operator signifies that the subsequent operation will round a numerical value.
<expression>: This represents the numerical expression or field reference to be rounded.
<decimalPlaces>: This specifies the number of decimal places to which the value should be rounded.

📝 Example

⌨️ Input

Consider a collection named temperatures containing documents with fields location and temperature representing temperature readings. Here are sample documents from the temperatures collection:

Output

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[
  { "_id": ObjectId("609c26812e9274a86871bc6a"), "location": "New York", "temperature": 21.578 },
  { "_id": ObjectId("609c26812e9274a86871bc6b"), "location": "Los Angeles", "temperature": 18.942 },
  { "_id": ObjectId("609c26812e9274a86871bc6c"), "location": "Chicago", "temperature": 16.723 }
]

🔄 Aggregation

Suppose we want to round the temperature values to two decimal places. Here's how you can achieve this using the $round operator:

example.js

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db.temperatures.aggregate([
  {
    $project: {
      location: 1,
      roundedTemperature: { $round: ["$temperature", 2] }
    }
  }
])

🧩 Explanation

$project: This stage reshapes documents in the aggregation pipeline and includes or excludes fields as specified.
$round: Rounds the temperature field to two decimal places.

When discussing how the above aggregation works:

In the first document, the temperature value of 21.578 is rounded to 21.58.
In the second document, the temperature value of 18.942 is rounded to 18.94.
In the third document, the temperature value of 16.723 is rounded to 16.72.

💻 Output

Now, let's take a look at the output generated by the aggregation pipeline:

Output

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{ "_id": ObjectId("609c26812e9274a86871bc6a"), "location": "New York", "roundedTemperature": 21.58 }
{ "_id": ObjectId("609c26812e9274a86871bc6b"), "location": "Los Angeles", "roundedTemperature": 18.94 }
{ "_id": ObjectId("609c26812e9274a86871bc6c"), "location": "Chicago", "roundedTemperature": 16.72 }

📚 Use Cases

Data Presentation:

The $round operator is valuable for presenting numerical data with a specified level of precision, ensuring clarity and readability.
Financial Calculations:

When dealing with financial data, rounding values to a certain number of decimal places is often necessary to maintain accuracy.
Statistical Analysis:

In statistical computations, rounding values can help in simplifying results without sacrificing meaningfulness.

🎉 Conclusion

The $round operator in MongoDB's aggregation framework provides a straightforward solution for rounding numerical values to a specified number of decimal places. Whether you're presenting data, performing financial calculations, or conducting statistical analysis, mastering the usage of $round empowers you to manipulate numerical data effectively within MongoDB's aggregation pipelines.

With its intuitive syntax and practical applications, the $round operator proves to be a valuable asset for handling numerical data within MongoDB. Incorporate it into your aggregation pipelines to streamline data processing and enhance the presentation of your analysis results.