mongo / mongoose aggregation pipeline query for survey data - mongodb

Question

I am trying to write a query to get all of the results of some survey data stored in a mongo. The tricky part is some questions are radio questions with a single answer, and some questions are multi-select type questions, some are values that need to be averaged, so I want to perform different aggregations depending on the type of question.
The results are stored in a schema like this, with each item in the array being a survey response.
[
{
metaData: {
survey: new ObjectId("62206ea0b31be3535abac547")
},
answers: {
'question1': 'a',
'question2': 'a',
'question3': ['a','c'],
'question4': 3
},
createdAt: 2022-03-03T07:30:40.517Z,
},
{
metaData: {
survey: new ObjectId("62206ea0b31be3535abac547"),
},
answers: {
'question1': 'a',
'question2': 'b',
'question3': ['a','c'],
'question4': 2
},
createdAt: 2022-03-03T07:30:40.518Z,
},
{
metaData: {
survey: new ObjectId("62206ea0b31be3535abac547"),
},
answers: {
'question1': 'b',
'question2': 'c',
'question3': ['b']
'question4': 1
},
createdAt: 2022-03-03T07:30:40.518Z,
}
]
question1 and question2 are radio questions, so there can be only 1 answer, whereas question 3 is a multi-select, so the user can have multiple answers. Question 4 is a value that needs to be averaged.
I think there is some way to accomplish this in a single aggregation pipeline with some combination of facets, grouping, filters, projections, etc, but I am stuck.
I'd like to get a final result that looks like this
{
'question1' : {
'a' : 2,
'b' : 1
},
'question2' : {
'a' : 1,
'b' : 1,
'c' : 1,
},
'question3' : {
'a' : 2,
'b' : 1,
'c' : 2,
},
'question4' : 2 //avg (3+2+1)/3
}
OR even better:
{
'radio': {
'question1' : {
'a' : 2,
'b' : 1
},
'question2' : {
'a' : 1,
'b' : 1,
'c' : 1,
},
},
'multi': {
'question3' : {
'a' : 2,
'b' : 1,
'c' : 2,
}
},
'avg' : {
'question4' : 2
}
}
My pipeline would look something like this:
Response.aggregate([
{ $match: { 'metaData.survey': surveyId} }, // filter only for the specific survey
{ $project: { // I assume I have to turn the answers into an array
"answers": { $objectToArray: "$answers" },
"createdAt": "$createdAt"
}
},
// maybe facet here?
// conceptually, In the next stage I'd want to bucket the questions
// by type with something like below, then perform the right type of
// aggregation depending on the question type
// if $in [$$answers.k ['question1, 'question2']] group by k, v and count
// if $in [$$answers.k ['question3']] unwind and count each unique value?
// { $facet : { radio: [], multi:[]}}
])
Basically, I know which question Id is a radio or a multi-select, I'm just trying to figure out how to format the pipeline to achieve the desired output based on the questionId being in a known array.
Bonus points if I can figure out how to also group the by day/month based on the createdAt time

Answer 1

db.collection.aggregate([
{
$match: {}
},
{
$project: { answers: { $objectToArray: "$answers" } }
},
{
$unwind: "$answers"
},
{
$unwind: "$answers.v"
},
{
$group: {
_id: "$answers",
c: { "$sum": 1 }
}
},
{
$group: {
_id: "$_id.k",
v: { "$push": { k: "$_id.v", v: "$c" } }
}
},
{
$group: {
_id: null,
v: { "$push": { k: "$_id", v: { "$arrayToObject": "$v" } } }
}
},
{
$set: { v: { $arrayToObject: "$v" } }
},
{
$replaceWith: "$v"
}
])
mongoplayground
db.collection.aggregate([
{
$match: {}
},
{
$project: { answers: { $objectToArray: "$answers" } }
},
{
$unwind: "$answers"
},
{
$set: {
"answers.type": {
$switch: {
branches: [
{
case: { $isArray: "$answers.v" },
then: "multi"
},
{
case: { $eq: [ { $type: "$answers.v" }, "string" ] },
then: "radio"
},
{
case: { $isNumber: "$answers.v" },
then: "avg"
}
],
default: "other"
}
}
}
},
{
$unwind: "$answers.v"
},
{
$group: {
_id: "$answers",
c: { $sum: 1 }
}
},
{
$group: {
_id: "$_id.k",
type: { $first: "$_id.type" },
v: {
$push: {
k: { $toString: "$_id.v" },
v: "$c"
}
}
}
},
{
$group: {
_id: "$type",
v: {
$push: {
k: "$_id",
v: { $arrayToObject: "$v" }
}
}
}
},
{
$group: {
_id: null,
v: {
$push: {
k: "$_id",
v: { $arrayToObject: "$v" }
}
}
}
},
{
$set: { v: { $arrayToObject: "$v" } }
},
{
$replaceWith: "$v"
},
{
$set: {
avg: {
$arrayToObject: {
$map: {
input: { $objectToArray: "$avg" },
as: "s",
in: {
k: "$$s.k",
v: {
$avg: {
$map: {
input: { $objectToArray: "$$s.v" },
as: "x",
in: { $multiply: [ { $toInt: "$$x.k" }, "$$x.v" ] }
}
}
}
}
}
}
}
}
}
])
mongoplayground