MongoDb group by combined with multiple sums and match - mongodb

Question

I have the fields, group_id, code, revenue. I want to do an aggregation where the revenue is grouped by the group_id and summed up for each type of code. Also, some of the codes will have a combined revenue. So for example, for codes "abc" and "ghi", there will be a combined revenue with header "agi". How do I do this?
If the input like
[
{
"group_id": "ABC",
"revenue": 100,
"code": "abc"
},
{
"group_id": "ABC",
"revenue": 200,
"code": "abc"
},
{
"group_id": "ABC",
"revenue": 200,
"code": "def"
},
{
"group_id": "ABC1",
"revenue": 200,
"code": "def"
},
{
"group_id": "ABC",
"revenue": 200,
"code": "def"
},
{
"group_id": "ABC1",
"revenue": 200,
"code": "abc"
},
{
"group_id": "ABC",
"revenue": 200,
"code": "ghi"
}
]
then the output will be
[
{
"group_id": "ABC",
"expenses": [
{
"code": "agi",
"revenue": 500
},
{
"code": "def",
"revenue": 400
}
]
},
{
"group_id": "ABC1",
"expenses": [
{
"code": "abc",
"revenue": 200
},
{
"code": "def",
"revenue": 200
}
]
},
]

Answer 1

Then group by group_id and code like this:
let combine = ["abc", "ghi"];
db.items.aggregate([
{
$addFields: {
code: {
$cond: {
if: { $in: ["$code", combine] },
then: "agi",
else: "$code"
}
}
}
},
{
$group: {
_id: {
group_id: "$group_id",
code: "$code"
},
revenue: { $sum: "$revenue" }
}
},
{
$group: {
_id: "$_id.group_id",
expenses: {
$push: {
code: "$_id.code",
revenue: "$revenue"
}
}
}
}
]);
Output
/* 1 */
{
"_id" : "ABC",
"expenses" : [
{
"code" : "def",
"revenue" : 400
},
{
"code" : "agi",
"revenue" : 500
}
]
},
/* 2 */
{
"_id" : "ABC1",
"expenses" : [
{
"code" : "def",
"revenue" : 200
},
{
"code" : "agi",
"revenue" : 200
}
]
}