Mongo DB aggregation result in the provided manner - mongodb

Question

the following data in my mongo-db
Input:
[
{
'id':1,
"year": "2022-10-01",
"Area":{
"Education":'Engineering'
}
},
{
'id':2,
"year": "2022-10-01",
"Area":{
"Education":'Commerce'
}
},
{
'id':3,
"year": "2022-10-01",
"Area":{
"Education":'Arts'
}
},
{
'id':4,
"year": "2022-10-01",
"Area":{
"Education":'Arts'
}
},
{
'id':5,
"year": "2022-01-01",
"Area":{
"Education":'Engineering'
}
},
{
'id':6,
"year": "2022-01-01",
"Area":{
"Education":'Engineering'
}
}
]
there are records of several years based on each Education field, final result to be in this form where first is grouped by date and then grouped by Education field and the count of each education field in each year
Outcome in this manner:
{
"2022-10-01": {
"Education": {
"Engineering": 1,
"Commerce": 1,
"Arts": 2
}
},
"2021-01-01": {
"Education": {
"Engineering": 2,
"Commerce": 0,
"Arts": 0
}
}
}

Answer 1

Try this one:
db.collection.aggregate([
{ $group: { _id: { year: "$year", Education: "$Area.Education" }, count: { $sum: 1 } } },
{ $group: { _id: "$_id.year", Education: { $push: { k: "$_id.Education", v: "$count" } } } },
{ $set: { k: "$_id", Education: { $arrayToObject: "$Education" } } },
{ $group: { _id: null, root: { $push: { k: "$_id", v: { Education: "$Education" } } } } },
{ $replaceWith: { $arrayToObject: "$root" } }
])
Mongo Playground
It is a bit difficult to count values which do not exist, because there could be infinite numbers of them. Maybe like this:
db.collection.aggregate([
{ $group: { _id: { year: "$year", Education: "$Area.Education" }, count: { $sum: 1 } } },
{ $group: { _id: "$_id.year", Education: { $push: { k: "$_id.Education", v: "$count" } } } },
{
$set: {
Education: {
$map: {
input: ["Engineering", "Arts", "Commerce"],
in: {
k: "$$this",
v: {
$let: {
vars: {
val: {
$first: {
$filter: {
input: "$Education",
as: "area",
cond: { $eq: ["$$this", "$$area.k"] }
}
}
}
},
in: { $ifNull: ["$$val.v", 0] }
}
}
}
}
}
}
},
{ $set: { k: "$_id", Education: { $arrayToObject: "$Education" } } },
{ $group: { _id: null, root: { $push: { k: "$_id", v: { Education: "$Education" } } } } },
{ $replaceWith: { $arrayToObject: "$root" } }
])