$maxN (Max N Accumulator)

Last updated: 2026-10-09

$maxN (Max N Accumulator)

$maxN is an accumulator returning an array of the N largest distinct values of a field in a group, available since MongoDB 5.2. No sort specification is needed — it takes the N largest values; result order is not guaranteed. Useful for per-group top-N value statistics.

📝 Syntax

{ $group: { _id: <key>, maxN: { $maxN: { input: <expression>, n: <number> } } } }

Returns：Array of the N largest distinct values in the group

▶ Example

Run the commands below in your local mongosh (requires a running mongod):

// $maxN: top 3 distinct scores per class
db.scores.aggregate([
  { $group: { _id: '$class', topScores: { $maxN: { input: '$score', n: 3 } } } }
])

Output：

{ "_id": "A", "topScores": [98, 95, 92] }

📌 Notes

• Requires MongoDB 5.2 or later
• Deduplicates automatically — a set of distinct maxima
• Unlike $topN, $maxN returns values only, not sorted documents

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❓ FAQ

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