Update Sum columns (#46542)

* Update SumColumns.cs

* Update Program.cs

* Update how-to-query-files-and-directories.md

* Update how-to-query-files-and-directories.md

---------

Co-authored-by: Bill Wagner <[email protected]>

Author: davidmost

docs/csharp/linq/how-to-query-files-and-directories.md

@@ -129,5 +129,4 @@ The following text shows how to use the <xref:System.String.Split%2A> method to
 
 :::code language="csharp" source="./snippets/HowToFilesAndDirectories/SumColumns.cs" id="SumColumns":::
 
-If your file is a tab-separated file, just update the argument in the `Split` method to `\t`.
-  
+If your file is a tab-separated file, just update the argument in the `SumColumns.ProcessColumns` method to `\t`.

docs/csharp/linq/snippets/HowToFilesAndDirectories/Program.cs

@@ -32,7 +32,7 @@
 
 Console.WriteLine();
 Console.WriteLine("Sum Spreadsheet columns");
-SumColumns.SumCSVColumns("scores.csv");
+SumColumns.ProcessColumns("scores.csv", ",");
 
 static void FindFilesByExtension()
 {

docs/csharp/linq/snippets/HowToFilesAndDirectories/SumColumns.cs

@@ -1,117 +1,59 @@
 namespace HowToFilesAndDirectories;
 
 // <SumColumns>
-public class SumColumns
+public static class SumColumns
 {
-    public static void SumCSVColumns(string fileName)
+    public static void ProcessColumns(string filePath, string seperator)
     {
-        string[] lines = File.ReadAllLines(fileName);
-
-        // Specifies the column to compute.
-        int exam = 3;
-
-        // Spreadsheet format:
-        // Student ID    Exam#1  Exam#2  Exam#3  Exam#4
-        // 111,          97,     92,     81,     60
-
-        // Add one to exam to skip over the first column,
-        // which holds the student ID.
-        SingleColumn(lines, exam + 1);
-        Console.WriteLine();
-        MultiColumns(lines);
-    }
-
-    static void SingleColumn(IEnumerable<string> strs, int examNum)
-    {
-        Console.WriteLine("Single Column Query:");
-
-        // Parameter examNum specifies the column to
-        // run the calculations on. This value could be
-        // passed in dynamically at run time.
-
-        // Variable columnQuery is an IEnumerable<int>.
-        // The following query performs two steps:
-        // 1) use Split to break each row (a string) into an array
-        //    of strings,
-        // 2) convert the element at position examNum to an int
-        //    and select it.
-        var columnQuery = from line in strs
-                          let elements = line.Split(',')
-                          select Convert.ToInt32(elements[examNum]);
-
-        // Execute the query and cache the results to improve
-        // performance. This is helpful only with very large files.
-        var results = columnQuery.ToList();
-
-        // Perform aggregate calculations Average, Max, and
-        // Min on the column specified by examNum.
-        double average = results.Average();
-        int max = results.Max();
-        int min = results.Min();
-
-        Console.WriteLine($"Exam #{examNum}: Average:{average:##.##} High Score:{max} Low Score:{min}");
+        // Divide each exam into a group
+        var exams = from line in MatrixFrom(filePath, seperator)
+                    from score in line
+
+                    // Identify the column number
+                    let colNumber = Array.FindIndex(line, t => ReferenceEquals(score, t))
+
+                    // The first column is the student ID, not the exam score
+                    // so it needs to be excluded
+                    where colNumber > 0
+
+                    // Convert the score from string to int
+                    // Group by column number, i.e. one group per exam
+                    group double.Parse(score) by colNumber into g
+                    select new
+                    {
+                        Title = $"Exam#{g.Key}",
+                        Min = g.Min(),
+                        Max = g.Max(),
+                        Avg = Math.Round(g.Average(), 2),
+                        Total = g.Sum()
+                    };
+
+        foreach (var exam in exams)
+        {
+            Console.WriteLine($"{exam.Title}\t"
+            + $"Average:{exam.Avg,6}\t"
+            + $"High Score:{exam.Max,3}\t"
+            + $"Low Score:{exam.Min,3}\t"
+            + $"Total:{exam.Total,5}");
+        }
     }
 
-    static void MultiColumns(IEnumerable<string> strs)
+    // Transform the file content to an IEnumerable of string arrays
+    // like a matrix
+    private static IEnumerable<string[]> MatrixFrom(string filePath, string seperator)
     {
-        Console.WriteLine("Multi Column Query:");
-
-        // Create a query, multiColQuery. Explicit typing is used
-        // to make clear that, when executed, multiColQuery produces
-        // nested sequences. However, you get the same results by
-        // using 'var'.
+        using StreamReader reader = File.OpenText(filePath);
 
-        // The multiColQuery query performs the following steps:
-        // 1) use Split to break each row (a string) into an array
-        //    of strings,
-        // 2) use Skip to skip the "Student ID" column, and store the
-        //    rest of the row in scores.
-        // 3) convert each score in the current row from a string to
-        //    an int, and select that entire sequence as one row
-        //    in the results.
-        var multiColQuery = from line in strs
-                            let elements = line.Split(',')
-                            let scores = elements.Skip(1)
-                            select (from str in scores
-                                    select Convert.ToInt32(str));
-
-        // Execute the query and cache the results to improve
-        // performance.
-        // ToArray could be used instead of ToList.
-        var results = multiColQuery.ToList();
-
-        // Find out how many columns you have in results.
-        int columnCount = results[0].Count();
-
-        // Perform aggregate calculations Average, Max, and
-        // Min on each column.
-        // Perform one iteration of the loop for each column
-        // of scores.
-        // You can use a for loop instead of a foreach loop
-        // because you already executed the multiColQuery
-        // query by calling ToList.
-        for (int column = 0; column < columnCount; column++)
+        for (string? line = reader.ReadLine(); line is not null; line = reader.ReadLine())
         {
-            var results2 = from row in results
-                           select row.ElementAt(column);
-            double average = results2.Average();
-            int max = results2.Max();
-            int min = results2.Min();
-
-            // Add one to column because the first exam is Exam #1,
-            // not Exam #0.
-            Console.WriteLine($"Exam #{column + 1} Average: {average:##.##} High Score: {max} Low Score: {min}");
+            yield return line.Split(seperator, StringSplitOptions.TrimEntries);
         }
     }
 }
-/* Output:
-    Single Column Query:
-    Exam #4: Average:76.92 High Score:94 Low Score:39
 
-    Multi Column Query:
-    Exam #1 Average: 86.08 High Score: 99 Low Score: 35
-    Exam #2 Average: 86.42 High Score: 94 Low Score: 72
-    Exam #3 Average: 84.75 High Score: 91 Low Score: 65
-    Exam #4 Average: 76.92 High Score: 94 Low Score: 39
- */
+// Output:
+// Exam#1  Average: 86.08  High Score: 99  Low Score: 35   Total: 1033
+// Exam#2  Average: 86.42  High Score: 94  Low Score: 72   Total: 1037
+// Exam#3  Average: 84.75  High Score: 91  Low Score: 65   Total: 1017
+// Exam#4  Average: 76.92  High Score: 94  Low Score: 39   Total:  923
 // </SumColumns>