joins3

db.postcodes.aggregate([
      {
        $geoNear:
        {
          near: 
          {
            "type": "Point",
            "coordinates": [
              51.5156725,
              -0.727387
            ]},
          distanceField: "distance",
          num: 10000,
          maxDistance: 3000,
          spherical: true
        }
      },
      {
        $lookup: {
          from: "homeSales",
          localField: "postcode",
          foreignField: "address.postcode",
          as: "priceData"
        }
      },
      {
        $unwind: "$priceData"
      },

      {
        $group: 
        {
          _id: {$year: "$priceData.date"},
          highestPrice: {$max: "$priceData.amount"},
          lowestPrice: {$min: "$priceData.amount"},
          averagePrice: {$avg: "$priceData.amount"},
          priceStdDev: {$stdDevPop: "$priceData.amount"}
        }
      },
      {
        $project:
        {
          _id: 0,
          Year: "_id",
          highestPrice: 1,
          lowestPrice: 1,
          averagePrice: {$trunc: "$averagePrice"},
          priceStdDev: {$trunc: "$priceStdDev"}
        }
      },
      {
        $sort: 
        {
          "Year": -1
        }
      }
    ]);