More than one 'in' expression within $map - mongodb

Question

Been recently playing around with an array field within documents of a collection, and was wondering if I could apply more than one expression having in is specified in some way?
$project: {
"new_field": {
$map: {
input: "$test",
as: "item",
in: {$trim: {input: "$$item"}}
}
}
}
And trying to avoid performing another projection I was thinking of doing something like this, but just fails with An object representing an expression must have exactly one field.
$project: {
"new_field": {
$map: {
input: "$test",
as: "item",
in: {$trim: {input: "$$item"}, $concat: ["$$item", "testing"]}
}
}
}
Is my only option to just do another project step with all the fields?

Answer 1

You could apply more than one operation. But the output will not be on top of the first expression' result.
Sample Query:
db.collection.aggregate([
{
$project: {
adjustedGrades: {
$map: {
input: "$quizzes",
as: "grade",
in: [
{
$add: [
"$$grade",
2
]
},
{
$add: [
"$$grade",
3
]
}
]
}
}
}
}
])
Difference:
I specified in as array.
in: [
{
$add: [
"$$grade",
2
]
},
{
$add: [
"$$grade",
3
]
}
]
Sample input:
[
{
_id: 1,
quizzes: [
5,
6,
7
]
},
{
_id: 2,
quizzes: []
},
{
_id: 3,
quizzes: [
3,
8,
9
]
}
]
Sample output:
[
{
"_id": 1,
"adjustedGrades": [
[
7,
8
],
[
8,
9
],
[
9,
10
]
]
},
{
"_id": 2,
"adjustedGrades": []
},
{
"_id": 3,
"adjustedGrades": [
[
5,
6
],
[
10,
11
],
[
11,
12
]
]
}
]
Play