Практическое руководство. Подсчет вхождений слова в строке (LINQ)
Обновлен: Ноябрь 2007
В этом примере показано использование запроса LINQ для подсчета вхождений указанного слова в строке. Обратите внимание, что для выполнения подсчета сначала вызывается метод Split для создания массива слов. Метод Split снижает производительность. Если подсчет слов является единственной выполняемой операцией в строке, следует рассмотреть возможность использования методов Matches или IndexOf. Однако если производительность не критична или предложение уже разделено для выполнения других запросов, то имеет смысл использовать LINQ для подсчета слов или фраз.
Пример
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.
*/
Компиляция кода
Создайте проект Visual Studio, предназначенный для .NET Framework версии 3.5. По умолчанию в этом проекте имеется ссылка на файл System.Core.dll и директива using (C#) или оператор Imports (Visual Basic) для пространства имен System.Linq. При работе с проектами C# добавьте директиву using для пространства имен System.IO.
Скопируйте этот код в проект.
Нажмите клавишу F5, чтобы скомпилировать и выполнить программу.
Нажмите любую клавишу для выхода из окна консоли.