Why is my mongodb aggregation count being returned as a decimal?

Question

The following query

db.getCollection("xyzCollection").aggregate(
    [
     { $match:
           { "startDate": { $gte: ISODate("2021-01-21T00:00:00.000+0000") } , "markets": { $exists: true }} 
     },
     { $group: 
           { _id: "$sportName" , "count": { $sum: 1 } }
     },
    ]
)

returns the following output:

{ 
    "_id" : "Ice Hockey", 
    "count" : 138.0
}
{ 
    "_id" : "Basketball", 
    "count" : 141.0
}
{ 
    "_id" : "Cricket", 
    "count" : 14.0
}
{ 
    "_id" : "Volleyball", 
    "count" : 32.0
}
{ 
    "_id" : "Football", 
    "count" : 685.0
}

Why is this? And how can I make it return an int? I'm using Studio 3T 2020.10.1 to execute the query. I have already tried using $toInt (wrapping the "1" or wrapping the " { $sum: 1 } ") but as expected it didn't work - bad syntax.

Thanks.

See [Data Types in the mongo Shell](https://docs.mongodb.com/manual/core/shell-types/index.html#numberdecimal): *The mongo shell treats all numbers as floating-point values by default.* `$toInt` should work, how did you make it? — Wernfried Domscheit, Jan 21 '21 at 08:38
Not really helpful in my case because as stated in the documentation $toInt is "New in version 4.0." I tried and as expected (given I am not on 4.0 - from memory I am on 3.7) it didn't parse. — JL_SO, Jan 31 '21 at 21:56

Gibbs · Answer 1 · 2021-01-21T08:40:34.127

2

It will return int

Play

You could use $toInt in $project pipeline.

{
 $project: {
   sum: {$toInt :"$count" } 
 } 
}

sample

I think it's due to Robo3t/Studio3t

Thanks @wernfried for the reference to justify the behaviour.

edited Jan 21 '21 at 08:40

answered Jan 21 '21 at 03:16

Gibbs

21,904
13
74
138

If you try $group and $sum:1 it will do also. to me it's something else – Minsky Jan 21 '21 at 03:30
I think it's due to robo3t/studio3t – Gibbs Jan 21 '21 at 03:31
yeah, also, the OP is not trying to sum `$count`. If you mean adding a stage just for that, then is a crime... – Minsky Jan 21 '21 at 03:32

score 1 · Answer 2 · answered Jan 21 '21 at 03:49

If your query is executed by a javascript runtime (which is what usage of ISODate suggests since this is not an MQL construct), the (same) runtime that is rendering your results only has one numeric type and it's a floating point type.

Use a tool written in/utilizing another language that supports integer types.

Why is my mongodb aggregation count being returned as a decimal?

2 Answers2