sum of daily activities over a month of July MongoDB aggregate

Question

I need to get the sum of steps done per day in the month of July. I am expecting 31 results.

Here is a sample from the database:

/* 1 */
{
    "_id" : ObjectId("5ff0a5878da39cdbf696ffea"),
    "dateTime" : ISODate("2020-07-03T17:20:00.000Z"),
    "value" : "14"
}

/* 2 */
{
    "_id" : ObjectId("5ff0a5878da39cdbf696ffeb"),
    "dateTime" : ISODate("2020-07-03T17:43:00.000Z"),
    "value" : "57"
}

The "value" is the steps done.

Answer 1

And here is solution if you want to have the days with 0 count with abit of JS help ( you need to provide which month in jsMonth , and which year in jsDayCount ) :

mongos> db.d.find()
{ "_id" : ObjectId("5ff62e4484088fbb4acaf035"), "dateTime" : ISODate("2020-07-03T17:20:00Z"), "value" : "14" }
{ "_id" : ObjectId("5ff62e4484088fbb4acaf036"), "dateTime" : ISODate("2020-07-05T17:20:00Z"), "value" : "14" }
{ "_id" : ObjectId("5ff62e4484088fbb4acaf037"), "dateTime" : ISODate("2020-07-03T17:20:00Z"), "value" : "50" }
{ "_id" : ObjectId("5ff62e4484088fbb4acaf038"), "dateTime" : ISODate("2020-08-10T17:20:00Z"), "value" : "100" }
mongos> var jsMonth=7;var jsDayCount=new Date(2020, jsMonth , 0).getDate();
mongos> db.d.aggregate([ 
{$project:{ byDay:{$dayOfMonth:{date:"$dateTime",timezone:"+0200"}},_id:0 , val:{$toInt:"$value"} ,mon: {$month:{date:'$dateTime',timezone:"+0200"}}  }} ,{$match:{ mon:jsMonth   }}  ,
{$group:{_id:"$byDay" , perDayTotal:{$sum:"$val"}}}    , {$sort:{_id:1}}  , 
{$group:{_id:"total" , arr:{$push:{day:"$_id",perDay:"$perDayTotal"   }} }}  , 
{ $addFields:{ arr:{ $reduce:{ input:{$setDifference:[ {$range:[1,jsDayCount,1]} ,"$arr.day"  ]   }, initialValue:"$arr",in:{ $concatArrays: 
["$$value" ,[{day:"$$this", perDay:0  }] ]     }     }  }  } }   ,
{$unwind:"$arr"}, 
{$project:{_id:0 ,day:"$arr.day" ,    countPerDay:"$arr.perDay"}}   , $sort:{"day":1}} ])
{ "day" : 1, "countPerDay" : 0 }
{ "day" : 2, "countPerDay" : 0 }
{ "day" : 3, "countPerDay" : 64 }
{ "day" : 4, "countPerDay" : 0 }
{ "day" : 5, "countPerDay" : 14 }
{ "day" : 6, "countPerDay" : 0 }
{ "day" : 7, "countPerDay" : 0 }
{ "day" : 8, "countPerDay" : 0 }
{ "day" : 9, "countPerDay" : 0 }
{ "day" : 10, "countPerDay" : 0 }
{ "day" : 11, "countPerDay" : 0 }
{ "day" : 12, "countPerDay" : 0 }
{ "day" : 13, "countPerDay" : 0 }
{ "day" : 14, "countPerDay" : 0 }
{ "day" : 15, "countPerDay" : 0 }
{ "day" : 16, "countPerDay" : 0 }
{ "day" : 17, "countPerDay" : 0 }
{ "day" : 18, "countPerDay" : 0 }
{ "day" : 19, "countPerDay" : 0 }
{ "day" : 20, "countPerDay" : 0 }
{ "day" : 21, "countPerDay" : 0 }
{ "day" : 22, "countPerDay" : 0 }
{ "day" : 23, "countPerDay" : 0 }
{ "day" : 24, "countPerDay" : 0 }
{ "day" : 25, "countPerDay" : 0 }
{ "day" : 26, "countPerDay" : 0 }
{ "day" : 27, "countPerDay" : 0 }
{ "day" : 28, "countPerDay" : 0 }
{ "day" : 29, "countPerDay" : 0 }
{ "day" : 30, "countPerDay" : 0 }
mongos>