MongoDB Advanced Aggregation: Mastering $bucket

What is the $bucket Operator?

$bucket is an aggregation stage that categorizes documents into buckets based on specified boundaries.

It groups documents by evaluating an expression and placing each document into the appropriate bucket range.

• Requires an expression to evaluate each document.
• Defines boundaries to specify bucket ranges.
• Optionally includes a default bucket for out-of-range values.
• Outputs documents grouped by bucket with aggregated results.

Syntax and Parameters

The $bucket stage requires several parameters to function correctly.

Here is the basic structure:

• `groupBy`: The expression to group documents by.
• `boundaries`: An array of values defining bucket boundaries in ascending order.
• `default` (optional): A bucket label for documents that don't fit in any boundary.
• `output` (optional): Specifies the aggregation expressions for each bucket.

Practical Example: Categorizing Product Prices

Suppose you have a collection of products with a price field and want to categorize them into price ranges.

You can use $bucket to group products into buckets like low, medium, and high price ranges.

Example Code

This example groups products by price into three buckets: less than $100, $100 to $500, and above $500.