mongo group query how to keep fields

By the way, if you want to keep not only the first document, you can use$addToSet For example:

db.test.aggregate({
  $group: {
    _id: '$name',
    name : { $addToSet: '$name' }
    age : { $addToSet: '$age' },
    count: { $sum: 1 }
  }
}

[edited to include comment suggestions]

I came here looking for an answer but wasn't happy with the selected answer (especially given it's age). I found this answer that is a better solution (adapted):

db.test.aggregate({
  $group: {
    _id: '$name',
   person: { "$first": "$$ROOT" },
   count: { $sum: 1 }
  },
  {
    "$replaceRoot": { "newRoot": { "$mergeObjects": ["$person", { count: "$count" }]} }
  }
}

If you want to keep the information about the first matching entries for each group, you can try aggregating like:

    db.test.aggregate([{
      $group: {
         _id : '$name',
         name : { $first: '$name' },
         age : { $first: '$age' },
         sex : { $first: '$sex' },
         province : { $first: '$province' },
         city : { $first: '$city' },
         area : { $first: '$area' },
         address : { $first: '$address' },
         count : { $sum: 1 },
      }
    }]);

You can try out this

db.test.aggregate({
      { $group: 
            { _id: '$name',count: { $sum: 1 }, data: { $push: '$$ROOT' } } },
      {
        $project: {
          _id:0,
          data:1,
          count :1
        }
      }

}