Group By Hour using UNIX time stamp in mongodb - mongodb

Question

I required records with the output of gender, count, and updated hour for two days.
db.FaceData.aggregate([ {$match: { 'Timestamp' : { $gte : 1448121600000, $lt : 1448294399000 }, 'DID' : "ABFR001" }}, {$group: { _id: {'Gen': '$Gen'}, count : { $sum : 1 } }} ]);
output:
------
{ "_id" : { "Gen" : 1 }, "count" : 3055 }
{ "_id" : { "Gen" : 0 }, "count" : 2866 }
In the above output I have to group by hour for two days, For Example, Every hour I need Gender, Count for 2days.
Timestamp is in millisecond.

Answer 1

You would need a mechanism to get the actual date object from the unix timestamp, one way is to add the timestamp to a zero-milliseconds Date() object, using the $add operator in the $project stage before the actual grouping aggregation pipeline.
Once you get the date, extract the hour part by using the $hour operator, something like the following:
db.FaceData.aggregate([
{
"$match": {
"Timestamp" : { $gte : 1448121600000, $lt : 1448294399000 },
"DID" : "ABFR001"
}
},
{
$project : {
"hourPart" : {
"$hour": { "$add": [ new Date(0), "$Timestamp" ] }
},
"Gen": 1
}
},
{
"$group": {
"_id": "$hourPart",
"Gen_0_count" : {
"$sum": {
"$cond": [ { "$eq": [ "$Gen", 0 ] }, 1, 0 ]
}
},
"Gen_1_count" : {
"$sum": {
"$cond": [ { "$eq": [ "$Gen", 1 ] }, 1, 0 ]
}
}
}
}
]);

Answer 2

{"$match": {
"Timestamp" : { $gte : 1448121600000, $lt : 1448294399000 },
"DID" : "ABFR001"
}} ,
{ "$group" : {
"_id" : {
"$divide" : [{ "$subtract" : [{"$divide" : ["$Timestamp", 1000]}, { "$mod" : [{"$divide" : ["$Tstmp", 1000]}, 3600] }] }, 3600 ]
},
"Male" : {
"$sum": {
"$cond": [ { "$eq": [ "$Gen", 0 ] }, 1, 0 ]
}
},
"Female" : {
"$sum": {
"$cond": [ { "$eq": [ "$Gen", 1 ] }, 1, 0 ]
}
}
} }