Round #580

Calculate a moving 7-day average of daily_sales using a window function.

```csharp using System; using System.Collections.Generic; using System.Linq; public class SalesData { public DateTime Date { get; set; } public int DailySales { get; set; } } class Program { static void Main() { // Create a sample list of sales data var salesData = new List<SalesData> { new SalesData { Date = DateTime.Parse("2022-01-01"), DailySales = 100 }, new SalesData { Date = DateTime.Parse("2022-01-02"), DailySales = 120 }, new SalesData { Date = DateTime.Parse("2022-01-03"), DailySales = 110 }, new SalesData { Date = DateTime.Parse("2022-01-04"), DailySales = 130 }, new SalesData { Date = DateTime.Parse("2022-01-05"), DailySales = 105 }, new SalesData { Date = DateTime.Parse("2022-01-06"), DailySales = 125 }, new SalesData { Date = DateTime.Parse("2022-01-07"), DailySales = 115 }, new SalesData { Date = DateTime.Parse("2022-01-08"), DailySales = 140 }, new SalesData { Date = DateTime.Parse("2022-01-09"), DailySales = 108 }, new SalesData { Date = DateTime.Parse("2022-01-10"), DailySales = 128 }, }; // Calculate the 7-day moving average var movingAverage = salesData.Select((x, i) => new { Date = x.Date, DailySales = x.DailySales, MovingAverage = salesData.Skip(Math.Max(0, i - 6)).Take(7).Average(y => y.DailySales) }); // Print the results foreach (var item in movingAverage) { Console.WriteLine($"Date: {item.Date.ToString("yyyy-MM-dd")}, Daily Sales: {item.DailySales}, Moving Average: {item.MovingAverage}"); } } } ```

```csharp using System; using System.Data; using System.Linq; public class SalesData { public DateTime Date { get; set; } public decimal DailySales { get; set; } } public class SalesCalculator { public static DataTable CalculateMovingAverage(DataTable salesData) { // Ensure the data is sorted by date var sortedData = salesData.AsEnumerable().OrderBy(r => r.Field<DateTime>("Date")); // Calculate the moving average var movingAverages = sortedData.Select((row, index) => { var startDate = row.Field<DateTime>("Date"); var endDate = startDate.AddDays(-6); var windowData = sortedData.Where(r => r.Field<DateTime>("Date") >= endDate && r.Field<DateTime>("Date") <= startDate); var average = windowData.Average(r => r.Field<decimal>("DailySales")); return new { Date = startDate, MovingAverage = average }; }); // Create a new DataTable with the moving averages var result = new DataTable(); result.Columns.Add("Date", typeof(DateTime)); result.Columns.Add("MovingAverage", typeof(decimal)); foreach (var average in movingAverages) { result.Rows.Add(average.Date, average.MovingAverage); } return result; } } class Program { static void Main() { // Create a sample DataTable var salesData = new DataTable(); salesData.Columns.Add("Date", typeof(DateTime)); salesData.Columns.Add("DailySales", typeof(decimal)); salesData.Rows.Add(new DateTime(2022, 1, 1), 100m); salesData.Rows.Add(new DateTime(2022, 1, 2), 120m); salesData.Rows.Add(new DateTime(2022, 1, 3), 110m); salesData.Rows.Add(new DateTime(2022, 1, 4), 130m); salesData.Rows.Add(new DateTime(2022, 1, 5), 140m); salesData.Rows.Add(new DateTime(2022, 1, 6), 150m); salesData.Rows.Add(new DateTime(2022, 1, 7), 160m); salesData.Rows.Add(new DateTime(2022, 1, 8), 170m); salesData.Rows.Add(new DateTime(2022, 1, 9), 180m); salesData.Rows.Add(new DateTime(2022, 1, 10), 190m); // Calculate the moving average var movingAverages = SalesCalculator.CalculateMovingAverage(salesData); // Print the results foreach (DataRow row in movingAverages.Rows) { Console.WriteLine($"Date: {row["Date"]}, Moving Average: {row["MovingAverage"]}"); } } } ``` This C# code calculates a moving 7-day average of daily sales using a window function. It first sorts the sales data by date, then calculates the average sales for each 7-day window. The results are stored in a new DataTable, which is then printed to the console. The `SalesCalculator` class contains a static method `CalculateMovingAverage` that takes a DataTable of sales data as input and returns a new DataTable with the moving averages. The `Main` method in the `Program` class demonstrates how to use this method with a sample DataTable. Note that this implementation assumes that the input DataTable has columns named "Date" and "DailySales", and that the "Date" column contains DateTime values and the "DailySales" column contains decimal values. If your DataTable has different column names or data types, you may need to modify the code accordingly.