CODEWITHSUNDEEP
mongodbaggregation-framework
mheisig
mheisig

Reputation: 155

MongoDB Aggregation Sum on Objects in Array

I've seen a lot of answers on how to sum properties of objects in arrays within the array, but I'm trying to sum individual properties on an object in an array across documents. For example, given this document structure:

{
   "id": 1,
   "stats": [
     {
       "number": 100,
       "year": 2014
     },
     {
       "number": 200,
       "year": 2015
     }
]
},


{
   "id": 2,
   "stats": [
     {
       "number": 50,
       "year": 2014
     },
     {
       "number": 75,
       "year": 2015
     }
]
}

The desired output would be:

{
   "stats": [
     {
       "number": 150,
       "year": 2014
     },
     {
       "number": 275,
       "year": 2015
     }
}

I don't want to sum the number property of 2014 and 2015, I want to sum it across 2014 for both documents.

Upvotes: 5

Views: 7934

Answers (2)

RootHacker
RootHacker

Reputation: 1107

This will give you the desired output

db.getCollection('yourcollection').aggregate([
    { $unwind: "$stats" },
    { 
        $group: {
            _id: "$stats.year",
            number:{$sum:"$stats.number"}
        }
    },
    { 
        $group: {
          _id: null,  
          stats:{ $push:  {year:"$_id",number:"$number"}}
        }
    },
    {  
        $project:{stats:1,_id:0}
    }  
])

Upvotes: 0

Smita Ahinave
Smita Ahinave

Reputation: 1888

db.test.aggregate([
   {  $unwind: "$stats" },
   {
        $group: {
            _id:"$stats.year",
            number:{$sum:"$stats.number"}
        }
    },
    { 
        $group: {
          _id: 0,  
          stats:{ $push:  {year:"$_id",number:"$number"}}
        }
    },
    {  
        $project:{stats:1,_id:0}
    } ])

Upvotes: 8

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