Mongo query to group and calculate average with group by - mongodb

Question

I have a mongo collection mytopic with the following structure:
id : ObjectId
host: String
analytics: Object
topic_count : Array
name: String
mentions: Int
duration: Float
percentage: Float
I want to group by analytics.topic_count.name and return the average of duration for each user.
My expected output is :
Topic1: User1: <Average of duration for Topic1>
User2: <float>
User3: <float>
User4: <float>
User5: <float>
Topic2 User1: <float>
User2: <float>
User3: <float>
User4: <float>
User5: <float>
is it possible to get this kind of output. I am new to mongo and totally lost on this query. Any help is appreciated.
Thanks
Here is a partial export of my db collection:
[{
"_id": {
"$oid": "5edfd7a9c7152c8e6c708482"
},
"host": "user1",
"analytics": {
"topic_count": [
{
"name": "Topic1",
"mentions": 12,
"duration": 160.94,
"percentage": 5.76
},
{
"name": "Topic4",
"mentions": 9,
"duration": 108.14,
"percentage": 3.87
},
{
"name": "Topic3",
"mentions": 3,
"duration": 48.52,
"percentage": 1.74
},
{
"name": "Topic2",
"mentions": 8,
"duration": 95.5,
"percentage": 3.42
},
{
"name": "Topic5",
"mentions": 2,
"duration": 2.43,
"percentage": 0.09
},
{
"name": "Topic6",
"mentions": 4,
"duration": 55.75,
"percentage": 1.99
},
{
"name": "Topic7",
"mentions": 4,
"duration": 53.33,
"percentage": 1.91
},
{
"name": "Topic8",
"mentions": 4,
"duration": 45.37,
"percentage": 1.62
}
]
}
},{
"_id": {
"$oid": "5edfd7a9c7152c8e6c708483"
},
"host": "user1",
"analytics": {
"topic_count": [
{
"name": "Topic1",
"mentions": 14,
"duration": 209.85,
"percentage": 7.13
},
{
"name": "Topic4",
"mentions": 9,
"duration": 97.27,
"percentage": 3.31
},
{
"name": "Topic3",
"mentions": 3,
"duration": 37.13,
"percentage": 1.26
},
{
"name": "Topic2",
"mentions": 4,
"duration": 52.46,
"percentage": 1.78
},
{
"name": "Topic5",
"mentions": 2,
"duration": 3.13,
"percentage": 0.11
},
{
"name": "Topic6",
"mentions": 4,
"duration": 34,
"percentage": 1.16
},
{
"name": "Topic7",
"mentions": 4,
"duration": 79.9,
"percentage": 2.72
},
{
"name": "Topic8",
"mentions": 4,
"duration": 87.45,
"percentage": 2.97
}
]
}
},{
"_id": {
"$oid": "5edfd7a9c7152c8e6c708484"
},
"host": "user1",
"analytics": {
"topic_count": [
{
"name": "Topic1",
"mentions": 12,
"duration": 165.19,
"percentage": 5.91
},
{
"name": "Topic4",
"mentions": 9,
"duration": 112.15,
"percentage": 4.01
},
{
"name": "Topic3",
"mentions": 3,
"duration": 29.28,
"percentage": 1.05
},
{
"name": "Topic2",
"mentions": 4,
"duration": 46.74,
"percentage": 1.67
},
{
"name": "Topic5",
"mentions": 3,
"duration": 2.7,
"percentage": 0.1
},
{
"name": "Topic6",
"mentions": 4,
"duration": 17.59,
"percentage": 0.63
},
{
"name": "Topic7",
"mentions": 4,
"duration": 62.34,
"percentage": 2.23
},
{
"name": "Topic8",
"mentions": 4,
"duration": 57.62,
"percentage": 2.06
}
]
}
},{
"_id": {
"$oid": "5edfd7a9c7152c8e6c708485"
},
"host": "user1",
"analytics": {
"topic_count": [
{
"name": "Topic1",
"mentions": 12,
"duration": 226.65,
"percentage": 6.04
},
{
"name": "Topic4",
"mentions": 9,
"duration": 139.59,
"percentage": 3.72
},
{
"name": "Topic3",
"mentions": 3,
"duration": 44.85,
"percentage": 1.2
},
{
"name": "Topic2",
"mentions": 4,
"duration": 69.18,
"percentage": 1.84
},
{
"name": "Topic5",
"mentions": 2,
"duration": 18.07,
"percentage": 0.48
},
{
"name": "Topic6",
"mentions": 4,
"duration": 63.9,
"percentage": 1.7
},
{
"name": "Topic7",
"mentions": 4,
"duration": 57.19,
"percentage": 1.52
},
{
"name": "Topic8",
"mentions": 4,
"duration": 60.42,
"percentage": 1.61
}
]
}
},{
"_id": {
"$oid": "5edfd7a9c7152c8e6c708486"
},
"host": "user1",
"analytics": {
"topic_count": [
{
"name": "Topic1",
"mentions": 12,
"duration": 181.99,
"percentage": 6.31
},
{
"name": "Topic4",
"mentions": 9,
"duration": 102.66,
"percentage": 3.56
},
{
"name": "Topic3",
"mentions": 3,
"duration": 33.21,
"percentage": 1.15
},
{
"name": "Topic2",
"mentions": 4,
"duration": 55.31,
"percentage": 1.92
},
{
"name": "Topic5",
"mentions": 5,
"duration": 9.24,
"percentage": 0.32
},
{
"name": "Topic6",
"mentions": 4,
"duration": 35.82,
"percentage": 1.24
},
{
"name": "Topic7",
"mentions": 4,
"duration": 72.24,
"percentage": 2.51
},
{
"name": "Topic8",
"mentions": 4,
"duration": 30.3,
"percentage": 1.05
}
]
}
}]

Answer 1

Are you looking for something like this ?
db.collection.aggregate([
{
"$unwind": "$analytics.topic_count"
},
{
"$group": {
"_id": {
topic: "$analytics.topic_count.name",
host: "$host"
},
"duration": {
"$avg": "$analytics.topic_count.duration"
}
}
},
{
"$group": {
"_id": "$_id.topic",
"durations": {
"$addToSet": {
"$mergeObjects": [
{
"host": "$_id.host"
},
{
"duration": "$duration"
}
]
}
}
}
}
])
Here is working Mongo Playground