Group count 2 item object array mongodb - mongodb

Question

I have the following array:
[
{
“counter”: 123456,
“user”: “USER1”,
“last”: “USER1”
},
{
“counter”: 123,
“user”: “USER1”,
“last”: “USER2”
},
{
“counter”: 111,
“user”: “USER2”,
“last”: “USER2”
},
{
“counter”: 1122,
“user”: “USER2”,
“last”: “USER2”
},
{
“counter”: 112233,
“user”: “USER1”,
“last”: “USER2”
},
]
I'm doing the following query on mongodb:
{$group: {
_id: “$user”,
total: {$sum: 1},
last: {$sum: {$cond: [
{$eq: ['$last’, '$user']}, 1, 0
]}}
}}
I would like to get the following result:
[
{
_id: “USER1”
total: 3,
last: 1
},
{
_id: “USER2”
total: 2,
last: 4
}
]
But I get this:
[
{
_id: “USER1”
total: 3,
last: 1
},
{
_id: “USER2”
total: 2,
last: 2
}
]
When I make the group I can not count the last item satisfactorily
How can I get the expected result? Thank you for your help.

Answer 1

You have only 2 "USER2" then can't $sum 4 $last on that _id.
try using compose _id if you need by index in user.
db.teste.aggregate([
{$group:{
_id: {user:"$user",last:"$last"},
total: {$sum:1},
last: {
$sum: {
$cond:[ {$eq: ["$last", user]}, 1, 0]
}
}
}}
])
If you need to add string or other occurrences in different fields. Query is:
db.teste.aggregate([
{$group:{
_id: "$user"
}},
{$lookup:{
from: "teste",
let: { indice: "$_id" },
pipeline: [
{$group:{
_id: null,
user:{$sum:{$cond:[
{$eq:["$user", "$$indice"]}, 1, 0
]}},
last:{$sum:{$cond:[
{$eq:["$last", "$$indice"]}, 1, 0
]}}
}},
{$project:{
_id: 0
}}
],
as: "res"
}}
])
From zero to hero:
//First we'll extract only what we need find, on this case distinct users
db.teste.aggregate([
{$group:{
_id: "$user"
}}
])
//Here we will get the indexes of the search and reinsert in our filter using $let (nodejs var)
db.teste.aggregate([
{$group:{
_id: "$user"
}},
{$lookup:{
from: "teste",
let: { indice: "$_id" },
pipeline: [],
as: "res"
}}
])
//Let's counter the total of reinserted elements
db.teste.aggregate([
{$group:{
_id: "$user"
}},
{$lookup:{
from: "teste",
let: { indice: "$_id" },
pipeline: [
{$group:{
_id: null,
total:{$sum:1}
}}
],
as: "res"
}}
])
//Now let's test a true condition
db.teste.aggregate([
{$group:{
_id: "$user"
}},
{$lookup:{
from: "teste",
let: { indice: "$_id" },
pipeline: [
{$group:{
_id: null,
user:{$sum:{$cond:[
{$eq:[true, true]}, 1, 0
]}}
}}
],
as: "res"
}}
])
//cond tested let's extract what we want
db.teste.aggregate([
{$group:{
_id: "$user"
}},
{$lookup:{
from: "teste",
let: { indice: "$_id" },
pipeline: [
{$group:{
_id: null,
user:{$sum:{$cond:[
{$eq:["$user", "$$indice"]}, 1, 0
]}},
last:{$sum:{$cond:[
{$eq:["$last", "$$indice"]}, 1, 0
]}}
}}
],
as: "res"
}}
])
//Let's take the _id of the sub-colection because we do not need it
db.teste.aggregate([
{$group:{
_id: "$user"
}},
{$lookup:{
from: "teste",
let: { indice: "$_id" },
pipeline: [
{$group:{
_id: null,
user:{$sum:{$cond:[
{$eq:["$user", "$$indice"]}, 1, 0
]}},
last:{$sum:{$cond:[
{$eq:["$last", "$$indice"]}, 1, 0
]}}
}},
{$project:{
_id: 0
}}
],
as: "res"
}}
])