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How to: Query for Characters in a String (LINQ) (Visual Basic)

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Because the String class implements the generic IEnumerable<T> interface, any string can be queried as a sequence of characters. However, this is not a common use of LINQ. For complex pattern matching operations, use the Regex class.

Example

The following example queries a string to determine the number of numeric digits it contains. Note that the query is "reused" after it is executed the first time. This is possible because the query itself does not store any actual results.

Class QueryAString

    Shared Sub Main()

        ' A string is an IEnumerable data source.
        Dim aString As String = "ABCDE99F-J74-12-89A"

        ' Select only those characters that are numbers
        Dim stringQuery = From ch In aString
                          Where Char.IsDigit(ch)
                          Select ch
        ' Execute the query
        For Each c As Char In stringQuery
            Console.Write(c & " ")
        Next

        ' Call the Count method on the existing query.
        Dim count As Integer = stringQuery.Count()
        Console.WriteLine(System.Environment.NewLine & "Count = " & count)

        ' Select all characters before the first '-'
        Dim stringQuery2 = aString.TakeWhile(Function(c) c <> "-")

        ' Execute the second query
        For Each ch In stringQuery2
            Console.Write(ch)
        Next

        Console.WriteLine(System.Environment.NewLine & "Press any key to exit")
        Console.ReadKey()
    End Sub
End Class
' Output:
' 9 9 7 4 1 2 8 9
' Count = 8
' ABCDE99F

Compile the code

Create a Visual Basic console application project, with an Imports statement for the System.Linq namespace.

See also