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。
C# 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.
*/