oh sorry, here. I would like to create variables for “Entry Date” and “Source” fields

[
  {
    $match:
      /**
       * query: The query in MQL.
       */
      {
        Source: "Clientx",
        "Entry Date": {
          $gte: ISODate(
            "2024-06-01T04:00:00.000+00:00"
          ),
          $lte: ISODate(
            "2024-07-01T04:00:00.000+00:00"
          ),
        },
      },
  },
  {
    $facet:
      /**
       * outputFieldN: The first output field.
       * stageN: The first aggregation stage.
       */
      {
        TotalClicks: [
          {
            $group: {
              _id: "$Source",
              TotalClicks: {
                $sum: 1,
              },
              TotalCost: {
                $sum: "$Cost",
              },
            },
          },
        ],
        UniqueIps: [
          {
            $group: {
              _id: "$IP Address",
            },
          },
          {
            $count: "UniqueIps",
          },
        ],
      },
  },
  {
    $unwind:
      /**
       * path: Path to the array field.
       * includeArrayIndex: Optional name for index.
       * preserveNullAndEmptyArrays: Optional
       *   toggle to unwind null and empty values.
       */
      {
        path: "$TotalClicks",
      },
  },
  {
    $unwind:
      /**
       * path: Path to the array field.
       * includeArrayIndex: Optional name for index.
       * preserveNullAndEmptyArrays: Optional
       *   toggle to unwind null and empty values.
       */
      {
        path: "$UniqueIps",
      },
  },
  {
    $project:
      /**
       * specifications: The fields to
       *   include or exclude.
       */
      {
        Source: "$TotalClicks._id",
        Total_Cost: "$TotalClicks.TotalCost",
        Total_Clicks: "$TotalClicks.TotalClicks",
        Unique_Clicks: "$UniqueIps.UniqueIps",
        Duplicate_Rate: {
          $concat: [
            {
              $toString: {
                $multiply: [
                  {
                    $round: [
                      {
                        $divide: [
                          {
                            $subtract: [
                              "$TotalClicks.TotalClicks",
                              "$UniqueIps.UniqueIps",
                            ],
                          },
                          "$TotalClicks.TotalClicks",
                        ],
                      },
                      4,
                    ],
                  },
                  100,
                ],
              },
            },
            "%",
          ],
        },
      },
  },
]