How to get the highest value of each date in a not finding MongoDb?

Question

In this case, the problem I'm having is to make a distinction of a list taking all the values of each registered day. Example:

{car: "Volvo", km:"101", dateInsert: : ISODate("2019-10-22T14:43:32.924+01:00")},

{car: "Volvo", km:"105", dateInsert: : ISODate("2019-10-22T14:50:32.924+01:00")},

{car: "Volvo", km:"115", dateInsert: : ISODate("2019-10-23T19:43:32.924+01:00")},

{car: "Volvo", km:"119", dateInsert: : ISODate("2019-10-23T20:30:32.924+01:00")},

{car: "BMW", km:"40", dateInsert: : ISODate("2019-10-10T14:43:32.924+01:00")},

{car: "BMW", km:"43", dateInsert: : ISODate("2019-10-10T14:50:32.924+01:00")},

{car: "BMW", km:"50", dateInsert: : ISODate("2019-10-10T19:43:32.924+01:00")},

{car: "BMW", km:"59", dateInsert: : ISODate("2019-10-11T20:30:32.924+01:00")}, ...

In this case is on bold showing only I need the last record of each day.

Whats is good way to get this records?

Answer 1

Test code here

MongoDB can compare documents also, by comparing the fields one by one, if they have same name, so putting km first field, we will get the max km first. $$ROOT is a system variable, has the value for all the document.

db.collection.aggregate([
  {
    "$group": {
      "_id": {
        "year": {
          "$year": "$dateInsert"
        },
        "day": {
          "$dayOfYear": "$dateInsert"
        }
      },
      "max": {
        "$max": {
          "km": "$km",
          "doc": "$$ROOT"
        }
      }
    }
  },
  {
    "$replaceRoot": {
      "newRoot": "$max.doc"
    }
  }
])

Answer 2

• $substr and $dateToString to extract only the date from the ISODate.
• $group and $addToSet to group all documents by the unique date.
• $reduce to find the document with maximum value of km field for each date.
• $project to project the result with proper fields

db.collection.aggregate([
  {
    "$set": {
      "dateInsert": {
        $substr: [
          {
            $dateToString: {
              date: "$dateInsert"
            }
          },
          0,
          10
        ]
      }
    }
  },
  {
    "$group": {
      "_id": "$dateInsert",
      "results": {
        $addToSet: {
          car: "$car",
          km: "$km"
        }
      }
    }
  },
  {
    "$set": {
      "results": {
        $reduce: {
          input: "$results",
          initialValue: {
            km: 0
          },
          in: {
            $cond: [
              {
                $gte: [
                  "$$this.km",
                  "$$value.km"
                ]
              },
              "$$this",
              "$$value"
            ]
          }
        }
      }
    }
  },
  {
    "$project": {
      dateInsert: "$_id",
      car: "$results.car",
      km: "$results.km",
      _id: 0
    }
  }
])

Here is the working example: https://mongoplayground.net/p/NkBxmdFT1_F