Comment : compter les occurrences d'un mot dans une chaîne (LINQ)

Cet exemple indique comment utiliser une requête LINQ pour compter les occurrences d'un mot spécifié dans une chaîne. Notez que pour effectuer le comptage, la méthode Split est d'abord appelée pour créer un tableau de mots. La méthode Split entraîne une baisse des performances. Si la seule opération sur la chaîne est de compter les mots, vous devez plutôt envisager l'utilisation des méthodes Matches ou IndexOf. Toutefois, si la question des performances n'est pas primordiale ou si vous avez déjà fractionné la phrase pour effectuer d'autres types de requêtes sur celle-ci, l'utilisation de LINQ pour compter les mots ou les expressions est pertinente.

Exemple

Class CountWords

    Shared Sub Main()

        Dim text As String = "Historically, the world of data and the world of objects" & 
                  " have not been well integrated. Programmers work in C# or Visual Basic" & 
                  " and also in SQL or XQuery. On the one side are concepts such as classes," & 
                  " objects, fields, inheritance, and .NET Framework APIs. On the other side" & 
                  " are tables, columns, rows, nodes, and separate languages for dealing with" & 
                  " them. Data types often require translation between the two worlds; there are" & 
                  " different standard functions. Because the object world has no notion of query, a" & 
                  " query can only be represented as a string without compile-time type checking or" & 
                  " IntelliSense support in the IDE. Transferring data from SQL tables or XML trees to" & 
                  " objects in memory is often tedious and error-prone."

        Dim searchTerm As String = "data"

        ' Convert the string into an array of words.
        Dim dataSource As String() = text.Split(New Char() {" ", ",", ".", ";", ":"}, 
                                                 StringSplitOptions.RemoveEmptyEntries)

        ' Create and execute the query. It executes immediately 
        ' because a singleton value is produced.
        ' Use ToLower to match "data" and "Data" 
        Dim matchQuery = From word In dataSource 
                      Where word.ToLowerInvariant() = searchTerm.ToLowerInvariant() 
                      Select word

        ' Count the matches.
        Dim count As Integer = matchQuery.Count()
        Console.WriteLine(count & " occurrence(s) of the search term """ & 
                          searchTerm & """ were found.")

        ' Keep console window open in debug mode.
        Console.WriteLine("Press any key to exit.")
        Console.ReadKey()
    End Sub
End Class
' Output:
' 3 occurrence(s) of the search term "data" were found.

class CountWords
{
    static void Main()
    {
        string text = @"Historically, the world of data and the world of objects" +
          @" have not been well integrated. Programmers work in C# or Visual Basic" +
          @" and also in SQL or XQuery. On the one side are concepts such as classes," +
          @" objects, fields, inheritance, and .NET Framework APIs. On the other side" +
          @" are tables, columns, rows, nodes, and separate languages for dealing with" +
          @" them. Data types often require translation between the two worlds; there are" +
          @" different standard functions. Because the object world has no notion of query, a" +
          @" query can only be represented as a string without compile-time type checking or" +
          @" IntelliSense support in the IDE. Transferring data from SQL tables or XML trees to" +
          @" objects in memory is often tedious and error-prone.";

        string searchTerm = "data";

        //Convert the string into an array of words
        string[] source = text.Split(new char[] { '.', '?', '!', ' ', ';', ':', ',' }, StringSplitOptions.RemoveEmptyEntries);

        // Create and execute the query. It executes immediately 
        // because a singleton value is produced.
        // Use ToLowerInvariant to match "data" and "Data" 
        var matchQuery = from word in source
                         where word.ToLowerInvariant() == searchTerm.ToLowerInvariant()
                         select word;

        // Count the matches.
        int wordCount = matchQuery.Count();
        Console.WriteLine("{0} occurrences(s) of the search term \"{1}\" were found.", wordCount, searchTerm);

        // Keep console window open in debug mode
        Console.WriteLine("Press any key to exit");
        Console.ReadKey();
    }
}
/* Output:
   3 occurrences(s) of the search term "data" were found.
*/

Compilation du code

• Créez un projet Visual Studio qui cible .NET Framework version 3.5. Par défaut, le projet possède une référence à System.Core.dll et une directive using (C#) ou une instruction Imports (Visual Basic) pour l'espace de noms System.Linq. Dans les projets C#, ajoutez une directive using pour l'espace de noms System.IO.

• Copiez ce code dans votre projet.

• Appuyez sur F5 pour compiler et exécuter le programme.

• Appuyez sur une touche pour quitter la fenêtre de console.

Voir aussi

Concepts

LINQ et chaînes