MongoDB - transform array field to set - mongodb

Question

I have documents with a field containing an array of values which can be duplicated. I want to transform these documents with an extra field corresponding to unique values of this array. I tried aggregate + addToSet without success.
Data:
{..., "random_integers" : [1, 1, 2, 2, 3, 3]},
{..., "random_integers" : [2, 3, 4, 4, 5, 6]},
{..., "random_integers" : [9, 9, 8, 8, 7, 7]}
Expecting:
{
...
"random_integers" : [1, 1, 2, 2, 3, 3],
"unique_integers" : [1, 2, 3],
},
{
...
"random_integers" : [2, 3, 4, 4, 5, 6],
"unique_integers" : [2, 3, 4, 5, 6],
},
{
...
"random_integers" : [9, 9, 8, 8, 7, 7],
"unique_integers" : [7, 8, 9],
}
Try with aggregate + addToSet():
# Query
db.getCollection().aggregate([
{
$group: {
_id: '$_id',
unique_integers: {$addToSet: '$random_integers' }
}
}
])
# Results
{..., "unique_integers" : [[1, 1, 2, 2, 3, 3]]},
{..., "unique_integers" : [[2, 3, 4, 4, 5, 6]]},
{..., "unique_integers" : [[9, 9, 8, 8, 7, 7]]}
$addToSet add the whole list into a set, instead of each element of the array. I tried to combine $addToSet with $each but it is not recognize by mongo on a group:
# Query
db.getCollection().aggregate([
{
$group: {
_id: '$_id',
unique_integers: {$addToSet: { $each: '$random_integers' }}
}
}
])
# Error
Error: command failed: {
"ok" : 0,
"errmsg" : "Unrecognized expression '$each'",
"code" : 168,
"codeName" : "InvalidPipelineOperator"
} : aggregate failed

Answer 1

db.ints.aggregate( [
{ $project: {
random_integers: 1,
unique_integers: { $setIntersection: [ "$random_integers", "$random_integers" ] },
_id: 0
} }
] )