Articles → MONGODB → $Bucket Aggregation Operator In Mongodb

$Bucket Aggregation Operator In Mongodb

This article describes the $bucket aggregation operator in MongoDB.

Purpose

The $bucket aggregation operator groups documents into a specified number of buckets based on the field value.

Syntax

{
  $bucket: {
    groupBy: <expression>,
    boundaries: [ <lower bound>, <upper bound> ],
    default: <value>,
    output: {
      <output1>: { <accumulator1> },
      ...
    }
  }
}

In the syntax above: -

Attribute	Description
groupBy	The field or expression used for grouping.
boundaries	An array of values that define the boundaries for the buckets. The array must be sorted in ascending order and contain at least two values.
default	The container for values outside the specified boundaries.
output	A document that defines the output for each bucket. You can use aggregation expressions and accumulators like $sum, $avg, $max, etc.

Example

Consider the following collection: -

Picture showing the sample document collection

We want to group the documents into three buckets, i.e., 0-10, 10-20, and 20-30. So, the query would be: -

db.sales.aggregate([
  {
    $bucket: {
      groupBy: "$price",
      boundaries: [0, 10, 20, 30],
      default: "Other",
      output: {
        Sum: { $sum: 1}
      }
    }
  }
])

Output

In the above picture, _id is the lower bound of the bucket where the document is grouped. It is also important to note that the lower bound is inclusive and the upper bound is exclusive when grouping the document into the bucket.

Since the upper bound is not included, the document with $price equal to 30 goes to the Other bucket.

Posted By -	Karan Gupta

Posted On -	Monday, June 10, 2024

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