how to perform statistics for every n elements in MongoDB - mongodb

Question

How to perform basic statistics for every n elements in Mongodb. For example, if I have total of 100 records like below
Name
Count
Sample
a
10
x
a
20
y
a
10
z
b
10
x
b
10
y
b
5
z
how do I perform mean, median, std dev for every 10 records so I get 10 results. So I want to calculate mean/median/std dev for A for every 10 sample till all the elements of database. Similarly for b, c and so on
excuse me if it is a naive question

Answer 1

you need to have some sort of counter to keep track of count.... for example I have added here rownumber then applied bucket of 3 (here n=3) and then returning the sum and average of the group(3). this example can be modified to do some sorting and grouping before we create the bucket to get the desired result.
Pls refer to https://mongoplayground.net/p/CL7vQGUWD_S
db.collection.aggregate([
{
$set: {
"rownum": {
"$function": {
"body": "function() {try {row_number+= 1;} catch (e) {row_number= 0;}return row_number;}",
"args": [],
"lang": "js"
}
}
}
},
{
$bucket: {
groupBy: "$rownum",
// Field to group by
boundaries: [
1,
4,
7,
11,
14,
17,
21,
25
],
// Boundaries for the buckets
default: "Other",
// Bucket id for documents which do not fall into a bucket
output: {
// Output for each bucket
"countSUM": {
$sum: "$count"
},
"averagePrice": {
$avg: "$count"
}
}
}
}
])