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$Bucket Aggregation Operator In Mongodb

Purpose

Syntax

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

1. groupBy → The field or expression to group by
2. boundaries → An array of values that specify the boundaries for the buckets. The array must be sorted in ascending order and contain at least two values
3. default → The bucket for values that do not fit in the specified boundaries
4. default → A document that specifies the output for each bucket. You can use aggregation expressions and accumulators like $sum, $avg, $max, etc.

Example

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

Output