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Cómo: Calcular valores de columna en un archivo de texto CSV (LINQ)

Actualización: noviembre 2007

Este ejemplo muestra cómo realizar cálculos de totales, como Suma, Media, Min y Max, sobre las columnas de un archivo .csv. Los principios del ejemplo que se muestran aquí se pueden aplicar a otros tipos de texto estructurado.

Para crear el archivo de origen

  • Copie las líneas siguientes en un archivo denominado scores.csv y guárdelo en su carpeta de solución. Suponga que la primera columna representa un identificador de alumno, y las columnas subsiguientes representan las calificaciones de cuatro exámenes.

    111, 97, 92, 81, 60
    112, 75, 84, 91, 39
    113, 88, 94, 65, 91
    114, 97, 89, 85, 82
    115, 35, 72, 91, 70
    116, 99, 86, 90, 94
    117, 93, 92, 80, 87
    118, 92, 90, 83, 78
    119, 68, 79, 88, 92
    120, 99, 82, 81, 79
    121, 96, 85, 91, 60
    122, 94, 92, 91, 91
    

Ejemplo

Class SumColumns

    Public Shared Sub Main()

        Dim lines As String() = System.IO.File.ReadAllLines("../../../scores.csv")

        ' Specifies the column to compute
        ' This value could be passed in at runtime.
        Dim exam = 3

        ' Spreadsheet format:
        ' Student ID    Exam#1  Exam#2  Exam#3  Exam#4
        ' 111,          97,     92,     81,     60
        ' one is added to skip over the first column
        ' which holds the student ID.
        SumColumn(lines, exam + 1)
        Console.WriteLine()
        MultiColumns(lines)

        ' Keep the console window open in debug mode.
        Console.WriteLine("Press any key to exit...")
        Console.ReadKey()

    End Sub

    Shared Sub SumColumn(ByVal lines As IEnumerable(Of String), ByVal col As Integer)

        ' This query performs two steps:
        ' split the string into a string array
        ' convert the specified element to
        ' integer and select it.
        Dim columnQuery = From line In lines _
                           Let x = line.Split(",") _
                           Select Convert.ToInt32(x(col))

        ' Execute and cache the results for performance.
        ' Only needed with very large files.
        Dim results = columnQuery.ToList()

        ' Perform aggregate calculations 
        ' on the column specified by col.
        Dim avgScore = Aggregate score In results Into Average(score)
        Dim minScore = Aggregate score In results Into Min(score)
        Dim maxScore = Aggregate score In results Into Max(score)

        Console.WriteLine("Single Column Query:")
        Console.WriteLine("Exam #{0}: Average:{1:##.##} High Score:{2} Low Score:{3}", _
                     col, avgScore, maxScore, minScore)


    End Sub

    Shared Sub MultiColumns(ByVal lines As IEnumerable(Of String))

        Console.WriteLine("Multi Column Query:")

        ' Create the query. It will produce nested sequences. 
        ' multiColQuery performs these steps:
        ' 1) convert the string to a string array
        ' 2) skip over the "Student ID" column and take the rest
        ' 3) convert each field to an int and select that 
        '    entire sequence as one row in the results.
        Dim multiColQuery = From line In lines _
                            Let fields = line.Split(",") _
                            Select From str In fields Skip 1 _
                                        Select Convert.ToInt32(str)

        Dim results = multiColQuery.ToList()

        ' Find out how many columns we have.
        Dim columnCount = results(0).Count()

        ' Perform aggregate calculations on each column.            
        ' One loop for each score column in scores.
        ' We can use a for loop because we have already
        ' executed the multiColQuery in the call to ToList.

        For j As Integer = 0 To columnCount - 1
            Dim column = j
            Dim res2 = From row In results _
                       Select row.ElementAt(column)

            ' Perform aggregate calculations 
            ' on the column specified by col.
            Dim avgScore = Aggregate score In res2 Into Average(score)
            Dim minScore = Aggregate score In res2 Into Min(score)
            Dim maxScore = Aggregate score In res2 Into Max(score)

            ' Add 1 to column numbers because exams in this course start with #1
            Console.WriteLine("Exam #{0} Average: {1:##.##} High Score: {2} Low Score: {3}", _
                              column + 1, avgScore, maxScore, minScore)

        Next
    End Sub

End Class
' 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

class SumColumns
{
    static void Main(string[] args)
    {
        string[] lines = System.IO.File.ReadAllLines(@"../../../scores.csv");

        // 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
        // one is added to skip over the first column
        // which holds the student ID.
        SingleColumn(lines, exam + 1);
        Console.WriteLine();
        MultiColumns(lines);

        Console.WriteLine("Press any key to exit");
        Console.ReadKey();
    }

    static void SingleColumn(IEnumerable<string> strs, int examNum)
    {
        Console.WriteLine("Single Column Query:");

        // examNum specifies the column to run the 
        // calculations on. This could also be
        // passed in dynamically at runtime.             

        // columnQuery is a IEnumerable<int>
        // This query performs two steps:
        // 1) split the string into a string[]
        // 2) convert the specified element to
        //    int and select it.
        var columnQuery =
            from line in strs
            let x = line.Split(',')
            select Convert.ToInt32(x[examNum]);

        // Execute and cache the results for performance.
        // Only needed with very large files.
        var results = columnQuery.ToList();

        // Perform aggregate calculations 
        // on the column specified by examNum.
        double average = results.Average();
        int max = results.Max();
        int min = results.Min();

        Console.WriteLine("Exam #{0}: Average:{1:##.##} High Score:{2} Low Score:{3}",
                 examNum, average, max, min);
    }
    static void MultiColumns(IEnumerable<string> strs)
    {
        Console.WriteLine("Multi Column Query:");

        // Create the columnQuery. Explicit typing is used
        // to make clear that the columnQuery will produce 
        // nested sequences. You can also just use 'var'.
        // The columnQuery performs these steps:
        // 1) convert the string to a string[]
        // 2) skip over the "Student ID" column and take the rest
        // 3) convert each string to an int and select that 
        //    entire sequence as one row in the results.
        IEnumerable<IEnumerable<int>> query =
            from line in strs
            let x = line.Split(',')
            let y = x.Skip(1)
            select (from str in y
                    select Convert.ToInt32(str));

        // Execute and cache the results for performance.
        // ToArray could also be used here.
        var results = query.ToList();

        // Find out how many columns we have.
        int columnCount = results[0].Count();

        // Perform aggregate calculations on each column.            
        // One loop for each score column in scores.
        // We can use a for loop because we have already
        // executed the columnQuery in the call to ToList.
        for (int column = 0; column < columnCount; column++)
        {
            var res2 = from row in results
                       select row.ElementAt(column);
            double average = res2.Average();
            int max = res2.Max();
            int min = res2.Min();

            // 1 is added to column because Exam numbers
            // begin with 1
            Console.WriteLine("Exam #{0} Average: {1:##.##} High Score: {2} Low Score: {3}",
                          column + 1, average, max, 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
 */

Si su archivo es un archivo de valores separados por tabuladores, simplemente cambie el argumento del método Split por \t.

Compilar el código

  • Cree un proyecto de Visual Studio destinado a .NET Framework versión 3.5. De manera predeterminada, el proyecto incluye una referencia a System.Core.dll y una directiva using (C#) o una instrucción Imports (Visual Basic) para el espacio de nombres System.Linq.

  • Copie este código en el proyecto.

  • Presione F5 para compilar y ejecutar el programa.

  • Presione cualquier tecla para salir de la ventana de consola.

Vea también

Conceptos

LINQ y cadenas

LINQ y directorios de archivos