docs/csharp/linq/snippets/HowToFilesAndDirectories/SumColumns.cs - main - aprogrammer/dotnet-docs

docs/csharp/linq/snippets/HowToFilesAndDirectories/SumColumns.cs
117 строк4 KB
Bill Wagner
Finish freshness update / reorg on LINQ content (#40437)
24 апр 2024, 20:59
24 апр 2024, 20:59bc2d72c
namespace HowToFilesAndDirectories;

// <SumColumns>
public class SumColumns
{
    public static void SumCSVColumns(string fileName)
    {
        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}");
    }

    static void MultiColumns(IEnumerable<string> strs)
    {
        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'.

        // 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++)
        {
            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}");
        }
    }
}
/* 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
 */
// </SumColumns>