CODEWITHSUNDEEP
mongodbmongodb-queryaggregation-framework
Sweta Sharma
Sweta Sharma

Reputation: 483

Multilevel $group using mongodb

I am trying to get the count of all the different value of a key in my MongoDB. I am getting the count as well but i am getting it with 2 different objects.

{ "_id" : ObjectId("596f6e95b6a1aa8d363befeb"), produce:"potato","variety" : "abc", "state" : 'PA' }

{ "_id" : ObjectId("596f6e95b6a1aa8d363befec"), produce:"potato", "variety" : "abc", "state" : 'PA' }

{ "_id" : ObjectId("596f6e95b6a1aa8d363befed"), produce:"potato", "variety" : "def", "state" : 'IA' }

{ "_id" : ObjectId("596f6e95b6a1aa8d363befee"), produce:"potato", "variety" : "def", "state" : 'IA' }

{ "_id" : ObjectId("596f6e95b6a1aa8d363befef"), produce:"potato", "variety" : "abc", "state" : 'DA' }

{ "_id" : ObjectId("596f6e95b6a1aa8d363befeg"), produce:"potato", "variety" : "abc", "state" : 'DA' }

{ "_id" : ObjectId("596f6e95b6a1aa8d363befeh"), produce:"potato", "variety" : "def", "state" : 'DA' }

{ "_id" : ObjectId("596f6e95b6a1aa8d363befei"), produce:"potato", "variety" : "abc", "state" : 'IA' }

db.aggregate([


    {
       $match:{produce: "potato"}
    },
    {
       "$group":{
          "_id":{"variety":"$variety","state":"$state"},
          "count":{"$sum":1}
        }    
    },
    {
       "$group":{
           "_id":null,
                "counts":{
                    "$push": {"filterkey":"$_id.variety","state":"$_id.state","count":"$count"}
                }
         }
     },
])

Actual Result : - counts

[

    { filterkey: 'abc', state: 'PA', count: 2},
    { filterkey: 'abc', state: 'IA', count: 1},
    { filterkey: 'abc', state: 'DA', count: 2},
    { filterkey: 'def', state: 'IA', count: 2},
    { filterkey: 'def', state: 'DA', count: 1}
]

Expected Result : - counts

[

    { filterkey: 'abc', states:{'PA':2,'IA':1,'DA':2},
    { filterkey: 'def', states:{'IA':2,'DA':1}
]

Is there is some way to get the data like this?

Upvotes: 2

Views: 649

Answers (1)

Ashh
Ashh

Reputation: 46451

You need to use multilevel $group ing here. First you need to use $group with the variety and state fields and need to $sum to get total number of unique document per variety and state.

Then second you need to use $group with the variety to get the number of unique documents per variety.

And Finally $arrayToObject to flatten the states array. 

db.collection.aggregate([
  { "$match": { "produce": "potato" }},
  { "$group": {
    "_id": { "variety": "$variety", "state": "$state" },
    "count": { "$sum": 1 }
  }},
  { "$group": {
    "_id": "$_id.variety",
    "states": {
      "$push": {
        "k": "$_id.state",
        "v": "$count"
      }
    }
  }},
  { "$addFields": {
    "states": {
      "$arrayToObject": "$states"
    }
  }}
])

You can remove stages one by one here and can see what actually happens.

Output

[
  {
    "_id": "def",
    "states": {
      "DA": 1,
      "IA": 2
    }
  },
  {
    "_id": "abc",
    "states": {
      "DA": 2,
      "IA": 1,
      "PA": 2
    }
  }
]

Upvotes: 2

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