$minN (Min N Accumulator)
Last updated: 2026-10-09
$minN (Min N Accumulator)
$minN is an accumulator returning an array of the N smallest distinct values of a field in a group, available since MongoDB 5.2 — symmetric to $maxN. No sort specification is needed; result order is not guaranteed. Useful for per-group lowest-N statistics.
| Category | Accumulators |
|---|---|
| MongoDB Version | 5.2+ |
| Example Language | mongosh (Shell) |
📝 Syntax
{ $group: { _id: <key>, minN: { $minN: { input: <expression>, n: <number> } } } }Returns：Array of the N smallest distinct values in the group
▶ Example
Run the commands below in your local mongosh (requires a running mongod):
// $minN: bottom 3 distinct scores per class
db.scores.aggregate([
{ $group: { _id: '$class', lowScores: { $minN: { input: '$score', n: 3 } } } }
])Output：
{ "_id": "A", "lowScores": [41, 55, 60] }📌 Notes
- Requires MongoDB 5.2 or later
- Deduplicates automatically
- Unlike $bottomN, $minN returns values only, not sorted documents
🏷️ Related Tags
💡 Related Cases
More hands-on cases coming soon.
📚 Related Tutorials
❓ FAQ
QWhat is the difference between $minN and $bottomN?
A$minN takes the N smallest distinct values; $bottomN takes the N tail documents by a sortBy rule.
QAre results deduplicated?
AYes, duplicates collapse to one.
QCan n be 0?
AYes, it returns an empty array.
