MongoDB count value of attribute and group by month and year - mongodb

Question

I have documents in my mongodb and i try to count every same description i have and classify to month they created.
I want to return an array that include array of objects that includes month number with sub array of description value with the count.
I want to be able to choose which description value to count and choose by what year he will show me the data
for example this is my documents:
[
{
"username": "ron",
"skills": [
{
"rank": "high",
list: [
{
"subject": "Football"
},
{
"subject": "Swim"
}
]
},
{
"rank": "low",
list: [
{
"subject": "Baseball"
},
]
}
],
"duration": 0,
"date": ISODate("2021-07-24T12:05:27.127Z"),
"createdAt": ISODate("2021-07-24T12:05:49.985Z"),
"updatedAt": ISODate("2021-07-24T12:05:49.985Z"),
"__v": 0
},
{
"username": "john",
"skills": [
{
"rank": "low",
list: [
{
"subject": "Football"
},
]
}
],
"duration": 0,
"date": ISODate("2021-07-25T12:05:53.000Z"),
"createdAt": ISODate("2021-07-24T12:05:59.249Z"),
"updatedAt": ISODate("2021-07-24T12:05:59.249Z"),
"__v": 0
},
{
"username": "david",
"skills": [
{
"rank": "high",
list: [
{
"subject": "Football"
},
{
"subject": "Baseball"
}
]
},
{
"rank": "low",
list: [
{
"subject": "Swim"
},
]
}
],
"duration": 0,
"date": ISODate("2021-08-26T12:06:13.000Z"),
"createdAt": ISODate("2021-07-24T12:06:21.328Z"),
"updatedAt": ISODate("2021-07-24T12:06:21.328Z"),
"__v": 0
},
{
"username": "david",
"skills": [
{
"request": "high",
list: [
{
"subject": "Swim"
},
]
},
{
"request": "low",
list: [
{
"subject": "Football"
},
{
"subject": "Baseball"
},
]
}
],
"duration": 0,
"date": ISODate("2021-01-21T13:07:50.000Z"),
"createdAt": ISODate("2021-07-24T12:08:05.552Z"),
"updatedAt": ISODate("2021-07-24T12:14:51.285Z"),
"__v": 0
},
{
"username": "david",
"skills": [
{
"rank": "high",
list: [
{
"subject": "Football"
},
]
},
],
"duration": 0,
"date": ISODate("2022-01-21T13:07:50.000Z"),
"createdAt": ISODate("2022-07-24T12:08:05.552Z"),
"updatedAt": ISODate("2022-07-24T12:14:51.285Z"),
"__v": 0
}
]
The result I expect to get if i want to get match only the description that equal to "Football" or "Baseball":
{
[ {"month_number":7,"result":[{"description":'Football',"count":2},{"description":"Baseball","count":1}]},
{"month_number":8,"result":[{"description":'Football',"count":1}]}]
}
I'm new to mongodb ... so far I have been able to count how many there are of each value and display only the values I want but I do not know how to classify it into months depending on the year I choose.
I tried this:
db.exercises.aggregate([{$match:{ $and:[{description:{$in: ["Baseball","Football"]}}]}} ,{$group:{_id:"$description",count:{$sum:1}}}])
and this
db.exercises.aggregate(
[
{
$project:
{
_id: 0,
year: { $year: "$date" },
month: { $month: "$date" },
description:"$description"
}
},
{
$match:{$and:[{description:{$in: ["Baseball","Football","Swim"]},year:2021}]}
},
{$group:{_id:"$description" , count:{$sum:1}}}
]
)

Answer 1

You need add 1 more grouping i.e. by month.
Working playground
db.collection.aggregate([
{
$project: {
_id: 0,
year: {
$year: "$date"
},
month: {
$month: "$date"
},
description: "$description"
}
},
{
$match: {
$and: [
{
description: {
$in: [
"Baseball",
"Football",
"Swim"
]
},
year: 2021
}
]
}
},
{
$group: {
_id: {
description: "$description",
month: "$month"
},
count: {
$sum: 1
}
}
},
{
$group: {
_id: {
month_number: "$_id.month"
},
results: {
$push: {
description: "$_id.description",
count: "$count"
}
}
}
},
{
$project: {
_id: 0,
month_number: "$_id.month_number",
results: 1
}
}
])