MongoDB – Return Document with $max Value in Specific Field

aggregatemaxmongodb

I have a json file that has some football results. I need to calculate which team won the most away games, and how many wins there were.

My query is this:

db.football.aggregate(
{"$unwind": "$rounds"},
{"$unwind": "$rounds.matches"}, 

{"$project":
    {
        //"rounds.matches.team2.name":1,
        away_team: "$rounds.matches.team2.name",
        winner_away:
            { $cond: {if: {$gt:["$rounds.matches.score2","$rounds.matches.score1"] }, then:1,else :0} },
        _id:0   
    }
},
{"$group": {
    _id: {team_name:"$away_team"},
    total_wins: {$sum:"$winner_away"}
    }
}
)

and what I get is this:

{ "_id" : { "team_name" : "Stoke City" }, "total_wins" : 6 }
{ "_id" : { "team_name" : "Newcastle United" }, "total_wins" : 2 }
{ "_id" : { "team_name" : "Chelsea" }, "total_wins" : 7 }
{ "_id" : { "team_name" : "Everton" }, "total_wins" : 5 }
{ "_id" : { "team_name" : "Bournemouth" }, "total_wins" : 6 }
{ "_id" : { "team_name" : "Manchester United" }, "total_wins" : 7 }
{ "_id" : { "team_name" : "Liverpool" }, "total_wins" : 8 }
{ "_id" : { "team_name" : "Manchester City" }, "total_wins" : 7 }
{ "_id" : { "team_name" : "Leicester City" }, "total_wins" : 11 }

If I add this to get just team's with more wins name, and number of wins

{"$group": {
        _id: "$team_name",
        max_wins: {$max: "$total_wins"}
        }
    }

I get this

{ "_id" : null, "max_wins" : 11 }

Can someone tell me how to get the name as well? I can do it using sort, limit but this will not work in case of two or more teams having equal number of wins.

Best Answer

what I did was this: exported to a new collection temp and then, grouped by total_winds, sorted by ID and took first elements. It returns not only the very first, but all those being equal.

  db.temp.aggregate([
  {$group: {
      _id: "$total_wins",
      my_winner: {$push: "$$ROOT"}
  }},
  {$sort:{_id:-1}},
  {$limit:1}  ]).pretty()
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