操作說明：計算某個字在字串中出現的次數 (LINQ) (Visual Basic)
本例示範如何使用 LINQ 查詢計算字串中指定單字的出現次數。 請注意，執行計數要先呼叫 Split 方法來建立文字陣列。 Split 方法有效能成本。 如果字串上唯一的作業是計算字數，您應該考慮改用 Matches 或 IndexOf 方法。 不過，如果效能不是重要的問題，或您已分割句子對它執行其他類型的查詢，則使用 LINQ 計算單字或詞組才有意義。
範例
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.
編譯程式碼
使用 System.Linq 命名空間的 Imports 陳述式建立 Visual Basic 主控台應用程式專案。
