In my aggregation pipeline, after some previous aggregation, I end up with documents similar to these:
[
{
"_id": 0,
"group": "Electronics",
// other fields omitted for brevity
"articles": [
{
"name": "Gameboy",
// Even more fields omitted for brevity
"area": "Video Games"
},
{
"name": "Playstation",
"area": "Video Games"
},
{
"name": "Refrigerator",
"area": "White Goods"
}
]
},
{
"_id": 1,
"group": "Food",
"articles": [
{
"name": "Apple",
"area": "Fruit"
},
{
"name": "Pear",
"area": "Fruit"
}
]
}
]
I need to extract the unique area values from the arrays, while keeping the rest of the document intact (the articles aren't needed afterwards, though). The result should look like this:
[
{
"_id": 0,
"group": "Electronics",
// other fields...
"articleAreas": [ "Video Games", "White Goods" ]
},
{
"_id": 1,
"group": "Food",
"articleAreas": [ "Fruit" ]
}
]
My gut feeling is that there should be some way to use $addToSet similar to what can be done in $group stages, but I couldn't figure out how.
You can try $addFields stage and $setUnion operator to get unique values from array,
$addFields to add new field articleAreas$setUnion to get unique values form array of values from articles.areadb.collection.aggregate([
{
$addFields: {
articleAreas: {
$setUnion: "$articles.area"
}
}
}
])