How Do I get saperated counts while grouping on multiple fields mongodb aggregation? - mongodb

Question

I have the following documents in my candidate collection.
candidates = [
{
name: "amit",
age: 21,
city: 'pune'
}
{
name: "rahul",
age: 23,
city: 'pune'
},
{
name: "arjun",
age: 21,
city: 'pune'
},
{
name: "rakesh",
age: 23,
city: 'pune'
},
{
name: "amit",
age: 22,
city: 'nashik'
}
]
I want to group by age and city fields and count the documents based on its sum independent of each other
I tried following query
candidate.aggregate([
{$group: {_id: {age: '$age', city: '$city'}, count: {$sum: -1}}}
{$sort: {count: -1}},
{$limit: 10}
])
which gives me count of combine results of age and city.
what I want instead
{
ages: [
{
age: 21,
count: 2
},
{
age: 23,
count: 2
},
{
age: 21,
count: 1
}
],
cities: [
{
city: 'pune',
count: 4
},
{
city: 'nashik',
count: 1
}
]
}
thanks for any help.

Answer 1

You need to use $facet stage, with a $group stage per age, and another per city.
Here's the query :
db.collection.aggregate([
{
$facet: {
byCity: [
{
$group: {
_id: {
city: "$city"
},
count: {
$sum: 1
}
}
},
{
$sort: {
count: -1
}
},
{
$limit: 10
}
],
byAge: [
{
$group: {
_id: {
age: "$age",
},
count: {
$sum: 1
}
}
},
{
$sort: {
count: -1
}
},
{
$limit: 10
}
]
}
},
])
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