MongoDB Syntax error: What is the proper syntax for aggregate and group?

Question

I am trying to use Aggregate and $group to do an averaging.

But I am having this error "Error: Line 5: Unexpected token }"

I am struggling to get the correct brackets in place. Appreciate if anyone can assist.

db.db1.aggregate([
        {$match:{"budget":"medium"}},
        {$group:{
            "_id":{"budget":"$budget"},
            "AvgBirthYear":{$avg:{"$birth_year"}}
                }
         }
         ])

My raw data is like this

kmdreko · Accepted Answer · 2019-01-17 04:00:01Z

1

$avg:{"$birth_year"} isn't valid, you probably meant $avg: "$birth_year"

Also, you're only matching documents where the field "budget" is "medium" so you'll only get one group, is that intended?

Also, "_id":{"budget":"$budget"} works but can be simplified to "_id": "$budget"

answered Jan 17, 2019 at 4:00

kmdreko

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Jitendra · Accepted Answer · 2019-01-17 05:08:39Z

1

Try something like:

db.db1.aggregate([
        {
           $match:{
                "budget":"medium"
           }
        },
        {
           $group:{
             "_id":"$budget",
             "AvgBirthYear":{ $avg: "$birth_year" }
           }
        }
])

edited Jan 17, 2019 at 5:08

answered Jan 17, 2019 at 5:03

Jitendra

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