total register users of current month with each date - angularjs

Question

Here, date is register date and with simple group by I got result like this
[
{ date: '2019-09-01', count: 1 },
{ date: '2019-09-02', count: 3 },
{ date: '2019-09-04', count: 2 },
{ date: '2019-09-05', count: 5 },
// ...
]
But I want each and every date if on that date user is not register that display count as 0
[
{ date: '2019-09-01', count: 1 },
{ date: '2019-09-02', count: 3 },
{ date: '2019-09-03', count: 0 },
{ date: '2019-09-04', count: 0 },
// ...
]
If the user is not registered on 3 and 4 dates then displays 0 counts.
monthalldate = [ '2019-09-1', '2019-09-2', '2019-09-3', '2019-09-4', '2019-09-5', '2019-09-6', '2019-09-7', '2019-09-8', '2019-09-9',
'2019-09-10', '2019-09-11', '2019-09-12', '2019-09-13',.......,
'2019-09-30' ]
User.aggregate([
{ "$group": {
"_id": { "$substr": ["$createdOn", 0, 10] },
"count": { "$sum": 1 },
"time": { "$avg": "$createdOn" },
}},
{ "$sort": { "_id": 1 } },
{ "$project": { "date": "$_id", "createdOn": "$count" }},
{ "$group": { "_id": null, "data": { "$push": "$$ROOT" }}},
{ "$project": {
"data": {
"$map": {
"input": monthalldate,
"in": {
"k": "$$this",
"v": { "$cond": [{ "$in": ["$$this", "$data.date" ] }, 1, 0 ] }
}
}
}
}},
{ "$unwind": "$data" },
{ "$group": { "_id": "$data.k", "count": { "$sum": "$data.v" }}}
]).exec(function (err, montlysub) {
// console.log(montlysub);
});
But I got the wrong result
My user collection
{ "_id" : ObjectId("5a0d3123f954955f15fe88e5"), "createdOn" : ISODate("2019-11-16T06:33:07.838Z"), "name":"test" },
{ "_id" : ObjectId("5a0d3123f954955f15fe88e6"), "createdOn" : ISODate("2019-11-17T06:33:07.838Z"), "name":"test2" }

Answer 1

$project transforms input documents. If there is no user record for a particular month, there are no input documents to transform and you won't have any output for that month.
Ways around this:
Create a collection containing the months (only), then start by retrieving the desired date range from this collection and joining user documents to each month.
Add the missing zero data points in the application, either as the results are iterated or as a post-processing step prior to result rendering.