Get lowest per date from multiple arrays in mongodb - mongodb

Question

I've the following structure of docs:
{
"_id" : ObjectId("5786458371d24d924d8b4575"),
"uniqueNumber" : "3899822714",
"lastUpdatedAt" : ISODate("2016-07-13T20:11:11.000Z"),
"new" : [
{
"price" : 8.4,
"created" : ISODate("2016-07-13T13:11:28.000Z")
},
{
"price" : 10.0,
"created" : ISODate("2016-07-13T14:50:56.000Z")
}
],
"used" : [
{
"price" : 10.99,
"created" : ISODate("2016-07-08T13:46:31.000Z")
},
{
"price" : 8.59,
"created" : ISODate("2016-07-13T13:11:28.000Z")
}
]
}
Now I need to get a list that gives me the lowest price of each array per date.
So, as example:
{
"uniqueNumber" : 1234,
"prices" : {
"created" : 2016-07-08,
"minNew" : 123,
"minUsed" : 22
}
}
By now I've built the following query
db.getCollection('col').aggregate([
{
$match : {
"uniqueNumber" : "3899822714"
}
},
{
$unwind : "$used"
},
{
$project : {
"uniqueNumber" : "$uniqueNumber",
"price" : "$used.price",
"ts" : "$used.created"
}
},
{
$sort : { "ts" : 1 }
},
{
$group : {_id: "$uniqueNumber", priceOfMaxTS : { $min: "$price" }, ts : { $last: "$ts" }}
}
]);
But this one will only give me the lowest price for the highest date. I couldn't really find anything that pushes me to the right direction to get the desired result.
UPDATE
I've found a way to get the lowest price of the used array grouped by day with this query:
db.getCollection('col').aggregate([
{
$match : {
"uniqueNumber" : "3899822714"
}
},
{
$unwind : "$used"
},
{
$project : {
"asin" : "$uniqueNumber",
"price" : "$used.price",
"ts" : "$used.created",
"y" : { "$year" : "$used.created" },
"m" : { "$month" : "$used.created" },
"d" : { "$dayOfMonth" : "$used.created" }
}
},
{
$group : { _id : { "year" : "$y", "month" : "$m", "day" : "$d" }, minPriceOfDay : { $min: "$price" }}
}
]);
No I only need to find a way to do this also to the new array in the same query.