Aggregation query which returns other fields - mongodb

Question

I have data which looks like this.
{
"badgeId" : "ventura",
"date" : ISODate("2016-12-22T21:26:40.382+0000"),
"mistakes" : NumberInt(10)
}
{
"_id" : "a4usNGibIu",
"badgeId" : "dog",
"date" : ISODate("2016-12-21T21:26:40.382+0000"),
"mistakes" : NumberInt(10)
}
{
"_id" : ObjectId("580c77801d7723f3f7fe0e77"),
"badgeId" : "dog",
"date" : ISODate("2016-11-24T21:26:41.382+0000"),
"mistakes" : NumberInt(5)
}
I need documents grouped by badgeId where the mistakes is smallest and the corresponding date
I cannot use $min, $max, $first, $last on for the date in $group because I need the date from the row where mistakes is lowest.
I tried the following query where I am using $min, but it won't give the intended result as it will pick $min of the date
db.Badges.aggregate([
{
$match: otherMatchConditions
},
{
$group: {
_id: '$badgeId',
date: {
$min: '$date'
},
mistakes: {
$min: '$mistakes'
}
}
}
])

Answer 1

You may sort the results by mistakes and then take the corresponding $first of mistakes and date
[
{$sort: {mistakes: 1}},
{
$group: {
_id: '$badgeId',
date: {
$first: '$date'
},
mistakes: {
$first: '$mistakes'
}
}
}
]

Answer 2

I think your query is right but as you see dates are invalid here.
ISODate("2016-14-22T21:26:41.382+0000") and ISODate("2016-13-22T21:26:40.382+0000"),
in both dates you can see months is 13 and 14 , which is not valid month. Below are right data after putting in mongodb.
{
"_id" : ObjectId("580ca86c9a43fad551ba801f"),
"badgeId" : "ventura",
"date" : ISODate("2016-12-22T21:26:40.382Z"),
"mistakes" : 10
}
{
"_id" : "a4usNGibIu",
"badgeId" : "dog",
"date" : ISODate("2016-12-23T21:26:40.382Z"),
"mistakes" : 10
}
{
"_id" : ObjectId("580c77801d7723f3f7fe0e77"),
"badgeId" : "dog",
"date" : ISODate("2016-12-24T21:26:40.382Z"),
"mistakes" : 5
}
When applied your query
db.getCollection('COLLECTION_NAME').aggregate([
{
$group: {
_id: '$badgeId',
date: {
$min: '$date'
},
mistakes: {
$min: '$mistakes'
}
}
}
])
I got the below result.
{
"_id" : "dog",
"date" : ISODate("2016-12-23T21:26:40.382Z"),
"mistakes" : 5
}
{
"_id" : "ventura",
"date" : ISODate("2016-12-22T21:26:40.382Z"),
"mistakes" : 10
}