"result" : [
          {
                  "maxTemp" : 83,
                  "group_id" : "Florida"
          },
          {
                  "maxTemp" : 57,
                  "group_id" : "New Mexico"
          },
          {
                  "maxTemp" : 81,
                  "group_id" : "California"
          },
          {
                  "maxTemp" : 57,
                  "group_id" : "Vermont"
          }
  ],
  "ok" : 1

db.data.aggregate(
           {
             $group: {
                 _id: "$State"
               , maxTemp: { $max :"$Temperature"}
             }
           },
           { $project: {
                _id: 0,
                group_id:"$_id",
                maxTemp: "$maxTemp"
            }}
        ).result.forEach(function(match) {
            results.push(db.data.findOne(match));
        });

> results
[ null, null, null, null ]