Bucket Aggregation : ($bucket and $bucketAuto)

MongoDB gives us some amazing tools to group and analyze data easily. Two such tools are $bucket and $bucketAuto — they help us group data into ranges (just like dividing marks into grade categories)

• Introduction to Bucket Aggregation

When we have a lot of data (like marks of students or prices of products), we may want to group            them into categories or ranges. For example:

1. 0–50 marks = Fail

2. 51–75 = Average

3. 76–100 = Excellent

In MongoDB, we can do this using two special tools:

• $bucket – We choose the ranges (like 0–50, 51–75…)

• $bucketAuto – MongoDB automatically creates ranges

• Explanation

Explanation of $bucket

• You decide where each bucket starts and ends by setting boundary values.

• If a value doesn’t fall in any bucket, it goes to a default group (if defined).

• Best when you already know the categories or ranges you want.

Example:

boundaries: [0, 51, 76, 101]

This creates:

• Bucket 1: 0–50

• Bucket 2: 51–75

• Bucket 3: 76–100

Explanation of $bucketAuto

• MongoDB automatically calculates ranges by dividing the data into equal-sized groups (by document count).

• You just tell it how many buckets you want.

• Best when you don’t know the exact ranges, but want balanced grouping.

Example:

buckets: 3

MongoDB will divide all values into 3 buckets, each having almost the same number of documents.

• Procedure (Steps to Try)

Let’s try this with a students collection in MongoDB Compass or Shell.

 Sample Data: Students Collection

• Screenshots

 A) $bucket – Custom Ranges

Goal: Divide marks into ranges: 0–50, 51–75, 76–100

db.students.aggregate([
  {
    $bucket: {
      groupBy: "$marks",
      boundaries: [0, 51, 76, 101], // 0–50, 51–75, 76–100
      default: "Out of Range",
      output: {
        count: { $sum: 1 },
        names: { $push: "$name" }
      }
    }
  }
])

B) $bucketAuto – Automatic Buckets

Goal: Let MongoDB create 3 equal groups based on marks

db.students.aggregate([
  {
    $bucketAuto: {
      groupBy: "$marks",
      buckets: 3, // MongoDB will divide into 3 groups
      output: {
        count: { $sum: 1 },
        names: { $push: "$name" }
      }
    }
  }
])

• Future Scope – Why Learn This?

This is super useful for:

• Making charts and dashboards

• Creating grade systems or sales ranges

• Grouping user ages, prices, scores, and more

• Working with analytics and reports

Later on, you can even connect this with charting tools like MongoDB Charts or Power BI.

• Summary

Feature	$bucket	$bucketAuto
Type	Manual bucket ranges	Automatic bucket ranges
Use Case	You know the ranges	You don’t know exact ranges
Example Use	Grades, price categories	Auto grouping for reports

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Mayank Balyan

University: Shree Balaji University, Pune

School: School of Computer Studies

Course: BCA (Bachelor of Computer Applications)

Interests: NoSQL, MongoDB, and related technologies

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