Goal: Visualze the growth over time of a user base or any other element in a collection. A prerequisite is that every element has a date field - the date on which it was created.
Approach: We need to split our collection entries into series elements per day to then accumulate them together.
We can do this using the following query:
Note: Line 9 holds the date format configuration that could e.g. be changed to separate the dates by calender week, month, year or any other preferred date time1
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87{
"collection": "users",
"aggregate": [
{
"$group": {
"_id": {
"time": {
"$dateToString": {
"format": "%Y-%m-%d",
"date": "$_created"
}
}
},
"value": {
"$sum": 1
}
}
},
{
"$addFields": {
"_id": "$_id.time"
}
},
{
"$sort": [
{
"name": "_id",
"direction": 1
}
]
},
{
"$group": {
"_id": null,
"data": {
"$push": "$$ROOT"
}
}
},
{
"$addFields": {
"data": {
"$reduce": {
"input": "$data",
"initialValue": {
"total": 0,
"d": []
},
"in": {
"total": {
"$sum": [
"$$this.value",
"$$value.total"
]
},
"d": {
"$concatArrays": [
"$$value.d",
[
{
"_id": "$$this._id",
"value": "$$this.value",
"runningTotal": {
"$sum": [
"$$value.total",
"$$this.value"
]
}
}
]
]
}
}
}
}
}
},
{
"$unwind": "$data.d"
},
{
"$replaceRoot": {
"newRoot": "$data.d"
}
}
]
}
Our output is a table that contains every ‘new’ element count per day, as well as the then accumulated total value
1 | | date | value | runningTotal | |