Find the difference Between The Documents in single collection

Working with Data
,
#1

My goal is to find two random documents. Each document has a UserCount. The usercount difference between these two document

Actually, I’m getting an output below

{
    "UserCount": 10,
    "_id": 30,
},
{
    "UserCount": 22,
    "_id": 31,
},
{
    "UserCount": 30,
    "_id": 32,
},
{
    "UserCount": 35,
    "_id": 33,
}

expecting output below.

{
    "UserCount": 10,
    "_id": 30,
    "difference" : "12",
},
{
    "UserCount": 22,
    "_id": 31,
    "difference" : "8",
},
{
    "UserCount": 30,
    "_id": 32,
    "difference" : "5",
},
{
    "UserCount": 35,
    "_id": 33,
    "difference" : "0",
}

using MongoDB query, it is very difficult to solve this problem.

#2

It is very hard with any system because your problem is not well defined.

How do you get your differences of “12” for _id:30 ? Is it the difference between UserCount of _id:30 and UserCount of _id:31 ?

What do you mean by

Is it random? Or you want the difference between the next _id ?

If difference is the result of a subtraction why do you put it between quotes as a string?