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Type:
Improvement
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Resolution: Duplicate
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Priority:
Minor - P4
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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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Query
Given the following collection:
{ _id : 0, grid : [ [ 0, 0, 0, 0 ], [ 0, 1, 0, 1 ], [ 0, 0, 0, 2 ], [ 1, 0, 2, 3 ] ] }
{ _id : 1, grid : [ [ 0, 0, 0, 0 ], [ 0, 0, 0, 2 ], [ 0, 0, 0, 4 ], [ 0, 0, 4, 5 ] ] }
one would expect to be able to transpose it as follows:
db.coll.aggregate({$project: { grid : { $zip: { inputs: "$grid" } } } })
However, this results in the following error:
2017-02-09T13:51:59.786-0500 E QUERY [thread1] Error: command failed: {
"ok" : 0,
"errmsg" : "inputs must be an array of expressions, found string",
"code" : 34461,
"codeName" : "Location34461"
} : aggregate failed :
So, the stage needs to be written instead as:
{
"$project" : {
"grid" : {
"$zip" : {
"inputs" : [
{ "$arrayElemAt" : [ "$grid", 0 ] },
{ "$arrayElemAt" : [ "$grid", 1 ] },
{ "$arrayElemAt" : [ "$grid", 2 ] },
{ "$arrayElemAt" : [ "$grid", 3 ] }
]
}
},
}
This is unexpected, more verbose, and only works for arrays with fixed dimensions.
- duplicates
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SERVER-31991 Allow n-ary aggregation expressions to compute their array of arguments dynamically
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- Backlog
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- related to
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- Backlog
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