joins2

db.homeSales.aggregate([
  {
    $group: 
    {
      _id: {$year: "$date"},
      higestPrice: {$max: "$amount"},
      lowestPrice: {$min: "$amount"},
      averagePrice: {$avg: "$amount"},
      priceStdDev: {$stdDevPop: "$amount"}
    }
  },
  {
    $sort: {_id: 1}
  },
  {
    $project:
    {
      _id: 1,
      higestPrice: 1,
      lowestPrice: 1,
      averagePrice: {$trunc: "$averagePrice"},
      priceStdDev: {$trunc: "$priceStdDev"}
    }
  }
])