Count the objects inside of an array on each document MongoDB

Question

My documents are organized this way:

{
        "_id" : ObjectId("5ea899d7e7da54cabbc022e7"),
        "date" : ISODate("2018-01-27T00:00:00Z"),
        "vehicleid" : 32028,
        "points" : [
                {
                        "direction" : 225,
                        "location" : {
                                "type" : "Point",
                                "coordinates" : [
                                        -3.801898,
                                        -38.501078
                                ]
                        },
                        "odometer" : 134746396,
                        "routecode" : 0,
                        "speed" : 0,
                        "deviceid" : 148590,
                        "metrictimestamp" : ISODate("2018-01-27T23:32:03Z")
                }

Where points is an array of objects. I need to group this documents and return the amount of elements inside each array. I guess that is something like:

pipe = [ 
  {
    '$project':{
      "_id":0
    }
  },
  {
    '$group':{
      "_id":{
        "vehicleid":"$vehicleid",
        "date":"$date"
      },'count':{'$size':'points'}
    }
  }
         ]

Detail: I need to run this on pymongo.

pymongo.errors.OperationFailure: unknown group operator '$size', returns this error — JediJesus
– JediJesus, Commented Apr 29, 2020 at 23:03
It should be { 'count': { '$sum': { '$size': '$points' } } } — thammada.ts
– thammada.ts, Commented Apr 29, 2020 at 23:07

thammada.ts · Accepted Answer · 2020-04-29 23:11:08Z

3

You have to use $sum to sum the size of each array like this

  {
    "$group": {
      "_id": {
        "vehicleid": "$vehicleid",
        "date": "$date"
      },
      "count": { "$sum": { "$size": "$points" } }
    }
  }

answered Apr 29, 2020 at 23:11

thammada.ts

5,2653 gold badges26 silver badges35 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

prasad_ · Accepted Answer · 2020-04-30 05:17:57Z

1

You can use any of the following aggregation pipelines. You will get the size of the points array field. Each pipeline uses different approach, and the output details differ, but the size info will be same.

The code runs with PyMongo:

pipeline = [
    { 
        "$unwind": "$points" 
    },
    { 
        "$group": { 
            "_id": { "vehicleid": "$vehicleid", "date": "$date" }, 
            "count": { "$sum": 1 } 
        }
    }
]

pipeline = [
  { 
      "$addFields": { "count": { "$size": "$points" } }
  }
]

answered Apr 30, 2020 at 5:17

prasad_

14.4k2 gold badges27 silver badges44 bronze badges

Comments

Shuvro · Accepted Answer · 2020-04-29 23:19:31Z

0

You can follow this code

$group : {
       _id : {
        "vehicleid":"$vehicleid",
        "date":"$date"
         count: { $sum: 1 }
       }
    }

answered Apr 29, 2020 at 23:19

Shuvro

2423 silver badges7 bronze badges

Collectives™ on Stack Overflow

Count the objects inside of an array on each document MongoDB

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related