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$minN (array operator)![](/docs/v5.2/assets/link.svg)
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Definition![](/docs/v5.2/assets/link.svg)
New in version 5.2.
Returns the n
smallest values in an array.
Tip
See also:
Syntax![](/docs/v5.2/assets/link.svg)
$minN
has the following syntax:
{ $minN: { n: <expression>, input: <expression> } }
Field | Description |
---|---|
n | An expression that resolves to a
positive integer. The integer specifies the number of array elements
that $minN returns. |
input | An expression that resolves to the
array from which to return the minimal n elements. |
Behavior![](/docs/v5.2/assets/link.svg)
You cannot specify a value of
n
less than1
.$minN
filters outnull
values found in theinput
array.If the specified
n
is greater than or equal to the number of elements in theinput
array,$minN
returns all elements in theinput
array.If
input
resolves to a non-array value, the aggregation operation errors.If
input
contains both numeric and string elements, the numeric elements are sorted before string elements according to the BSON comparison order.
Example![](/docs/v5.2/assets/link.svg)
Create a scores
collection with the following documents:
db.scores.insertMany([ { "playerId" : 1, "score" : [ 1, 2, 3 ] }, { "playerId" : 2, "score" : [ 12, 90, 7, 89, 8 ] }, { "playerId" : 3, "score" : [ null ] }, { "playerId" : 4, "score" : [ ] }, { "playerId" : 5, "score" : [ 1293, "2", 3489, 9 ]} ])
The following example uses the $minN
operator to retrieve the two
lowest scores for each player. The lowest scores are returned in the new field
minScores
created by $addFields
.
db.scores.aggregate([ { $addFields: { minScores: { $minN: { n: 2, input: "$score" } } } } ])
The operation returns the following results:
[{ "playerId": 1, "score": [ 1, 2, 3 ], "minScores": [ 1, 2 ] }, { "playerId": 2, "score": [ 12, 90, 7, 89, 8 ], "minScores": [ 7, 8 ] }, { "playerId": 3, "score": [ null ], "minScores": [ ] }, { "playerId": 4, "score": [ ], "minScores": [ ] }, { "playerId": 5, "score": [ 1293, "2", 3489, 9 ], "minScores": [ 9, 1293 ] }]