joins3

var findNeighbours = function (spot, yearTag) {
  var result = db.postcodes.aggregate([
      {
        $geoNear:
        {
          near: spot,
          distanceField: "distance",
          num: 5,
          spherical: true
        }
      },
      {
        $group: {
          _id: yearTag,
          "neighbours": {
            $addToSet: "$postcode"
          }
        }
      }
    ]);
  return result.result;
}