MongoDB Query - Get frequency map of an array - mongodb

Question

[
{
"_id": ObjectId("id-1"),
"tests": [
{
"category": "cat1",
"status": "status1",
},
{
"category": "cat1",
"status": "status2",
},
{
"category": "cat2",
"status": "status2",
},
],
},
{
"_id": ObjectId("id-2"),
"tests": [
{
"category": "cat2",
"status": "status1",
},
{
"category": "cat1",
"status": "status1",
},
{
"category": "cat1",
"status": "status2",
},
],
}
]
I have the above collection, my intention is to generate the below result. Please note that the statuses and categories are dynamic.
[
{
"id" : id-1,
"status": {
"status1": count,
"status2": count
},
"category": {
"cat1": count of it,
"cat2": count of it
}
},
{
"id" : id-2,
"status": {
"status1": count of it,
"status2": count of it
},
"category": {
"cat1": count of it,
"cat2": count of it
}
}
]
What I've attempted to do till now, is
Unwinded tests field, then
{
"$group": {
"_id": {
"id": "$_id",
"testStatus": "$tests.status"
},
"val": {
"$sum": 1
}
}
},
{
"$group": {
"_id": {
"id": "$_id.id",
},
"resGroup": {
"$addToSet": {
k: "$_id.testStatus",
v: "$val"
}
}
}
},
{
"$project": {
"_id": "$_id.id",
"statusGroup": {
"$arrayToObject": "$resGroup"
}
}
}
I've done the same for the category field and used $facet to run multiple aggregations.
But, am unable to fetch the result in the required format.
Any help on this will be appreciated.
Thanks
MongoDB Version: 3.4

Answer 1

$map to iterate loop of tests array and convert the object to an array using $objectToArray
$unwind deconstruct tests array
$unwind again deconstruct tests array because it's a nested array
$group by _id, k, and v and get the total count
$group by _id and k and construct the array of the status field in items
$arrayToObject convert items key-value array to an object
$group by _id and construct the array of items
$arrayToObject convert items array to object
db.collection.aggregate([
{
$project: {
tests: {
$map: {
input: "$tests",
in: { $objectToArray: "$$this" }
}
}
}
},
{ $unwind: "$tests" },
{ $unwind: "$tests" },
{
$group: {
_id: {
_id: "$_id",
k: "$tests.k",
v: "$tests.v"
},
count: { $sum: 1 }
}
},
{
$group: {
_id: {
_id: "$_id._id",
k: "$_id.k"
},
items: {
$push: {
k: "$_id.v",
v: "$count"
}
}
}
},
{
$group: {
_id: "$_id._id",
items: {
$push: {
k: "$_id.k",
v: { $arrayToObject: "$items" }
}
}
}
},
{ $project: { items: { $arrayToObject: "$items" } } }
])
Playground