如何：对某词在字符串中出现的次数进行计数 (LINQ)
更新：2007 年 11 月
此示例演示如何使用 LINQ 查询来计数指定词在字符串中的出现次数。请注意，若要执行计数，请先调用 Split 方法来创建词数组。Split 方法存在性能开销。如果对字符串执行的唯一操作是计数词，则您应考虑改用 Matches 或 IndexOf 方法。但是，如果性能不是关键问题，或者您已拆分句子以对其执行其他类型的查询，则使用 LINQ 来计数词或短语同样有意义。
示例
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.
*/
编译代码
创建一个面向 .NET Framework 3.5 版的 Visual Studio 项目。默认情况下，该项目具有对 System.Core.dll 的引用，以及 System.Linq 命名空间的 using 指令 (C#) 或 Imports 语句 (Visual Basic)。在 C# 项目中，添加 System.IO 命名空间的 using 指令。
将此代码复制到您的项目。
按 F5 编译并运行程序。
按任意键退出控制台窗口。