Get last timestamp from an array in pymongo - mongodb

Question

I've got the following list of documents:
[
{'id': 1,
'name': 'Coco',
'data': [{'X': 10, 'datetime': datetime.datetime(2020, 1, 1, 1, 0)},
{'X': 20, 'datetime': datetime.datetime(2019, 1, 1, 2, 0)}]
},
{'id': 2,
'name': 'Kiki',
'data': [{'X': 30, 'datetime': datetime.datetime(2015, 7, 10, 1, 0)},
{'X': 40, 'datetime': datetime.datetime(2017, 10, 4, 2, 0)}]
]
How do I get the last timestamp from each list in the data field? I would like to get something like:
[
{'id': 1,
'name': 'Coco',
'data': [{'X': 10, 'datetime': datetime.datetime(2020, 1, 1, 1, 0)}]
},
{'id': 2,
'name': 'Kiki',
'data': [{'X': 40, 'datetime': datetime.datetime(2017, 10, 4, 2, 0)}]
]

Answer 1

Try this:
db.collectionName.aggregate([
{
$addFields: {
"data": [{
$reduce: {
input: "$data",
initialValue: { $arrayElemAt: ["$data", 0] },
in: {
$cond: [
{ $gt: ["$$value.datetime", "$$this.datetime"] },
"$$value",
"$$this"
]
}
}
}]
}
}
]);
Output:
/* 1 createdAt:3/3/2021, 9:15:27 PM*/
{
"_id" : ObjectId("603faf17bcece4372062bcf5"),
"id" : 1,
"name" : "Coco",
"data" : [
{
"X" : 10,
"datetime" : ISODate("2020-02-01T01:00:00.000+05:30")
}
]
},
/* 2 createdAt:3/3/2021, 9:15:27 PM*/
{
"_id" : ObjectId("603faf17bcece4372062bcf6"),
"id" : 2,
"name" : "Kiki",
"data" : [
{
"X" : 40,
"datetime" : ISODate("2017-11-04T02:00:00.000+05:30")
}
]
}