Group by Date mongoDB - mongodb

Question

I have a set of data in mongoDB that I have to sum up grouped by $timestamp. This field contains a date, but's formatted as String (example data above).
How should I proceed to convert $timestamp into a date so I can group them all together?
Next, I have to sum each scores_today for each date and iden, and the same with each scores_total.
Example data:
[
{
_id: "1442",
timestamp: "2016-03-15T22:24:02.000Z",
iden: "15",
scores_today: "0.000000",
scores_total: "52337.000000"
}
]
My code
var project = {
"$project":{
"_id": 0,
"y": {
"$year": "$timestamp" // tried this way, not working
},
"m": {
"$month": new Date("$timestamp") // tried either this, not working
},
"d": {
"$dayOfMonth": new Date("$timestamp")
},
"iden" : "$iden"
}
},
group = {
"$group": {
"_id": {
"iden" : "$iden",
"year": "$y",
"month": "$m",
"day": "$d"
},
"count" : { "$sum" : "$scores_today" }
}
};
mongoDB.collection('raw').aggregate([ project, group ]).toArray()....
This is the error logged by node.js service
Err: { [MongoError: exception: can't convert from BSON type String to
Date] name: 'MongoError', message: 'exception: can\'t convert from
BSON type String to Date', errmsg: 'exception: can\'t convert from
BSON type String to Date', code: 16006, ok: 0 }

Answer 1

You can construct Date object from string using ISODate($timestamp).
var project = {
"$project":{
"_id": 0,
"y": {
"$year": ISODate("$timestamp").getFullYear()
},
"m": {
"$month": ISODate("$timestamp").getMonth()+1 // months start from 0
},
"d": {
"$dayOfMonth": ISODate("$timestamp").getDate()
},
"iden" : "$iden"
}
},
group = {
"$group": {
"_id": {
"iden" : "$iden",
"year": "$y",
"month": "$m",
"day": "$d"
},
"count" : { "$sum" : "$scores_today" }
}
};
UPDATE
If you're not running MongoDb shell then you can't use ISODate directly. In this case try to invoke eval command.
var aggregationResult=mongoDB.eval(
'
'function() '+
'{ '+
' var project = { '+
' "$project":{ '+
' "_id": 0, '+
' "y": { '+
' "$year": ISODate("$timestamp").getFullYear() '+
' }, '+
' "m": { '+
' "$month": ISODate("$timestamp").getMonth()+1 // months start from 0 '+
' }, '+
' "d": { '+
' "$dayOfMonth": ISODate("$timestamp").getDate() '+
' }, '+
' "iden" : "$iden" '+
' } '+
' }, '+
' group = { '+
' "$group": { '+
' "_id": { '+
' "iden" : "$iden", '+
' "year": "$y", '+
' "month": "$m", '+
' "day": "$d" '+
' }, '+
' "count" : { "$sum" : "$scores_today" } '+
' } '+
' };
' var result=db.raw.aggregate([ project, group ]); '+
' return result; '+
' } '+
'
);