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Type:
New Feature
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Resolution: Duplicate
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: Aggregation Framework
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None
We have operators $first and $last, these accumulation operators allow you to select the first or last entries for a given value within a group operator.
Can we add a $first-n and $last-n operator which would return several of the last values in an array as such:
Initial Data
for(i=0;i<100;i++){db.t2.insert({name :"one", x:i})} for(i=0;i<100;i++){db.t2.insert({name :"two", x:i})} for(i=0;i<100;i++){db.t2.insert({name :"three", x:i})}
Aggregation command example
db.t2.aggregate([{$group: {_id:"$name", x :{ "$last" :["$x", 3]}}}])
Example output
{ "_id" : "three", "x" : [ 99, 98, 97 ] }
{ "_id" : "two", "x" : [ 99, 98, 97 ] }
{ "_id" : "one", "x" : [ 99, 98, 97 ] }
- duplicates
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SERVER-9377 Allow collecting "top" N values for each group
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- Closed
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