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How to query for characters in a string (LINQ) (C#)

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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  
{  
    static void Main()  
    {  
        string aString = "ABCDE99F-J74-12-89A";  
  
        // Select only those characters that are numbers  
        IEnumerable<char> stringQuery =  
          from ch in aString  
          where Char.IsDigit(ch)  
          select ch;  
  
        // Execute the query  
        foreach (char c in stringQuery)  
            Console.Write(c + " ");  
  
        // Call the Count method on the existing query.  
        int count = stringQuery.Count();  
        Console.WriteLine("Count = {0}", count);  
  
        // Select all characters before the first '-'  
        IEnumerable<char> stringQuery2 = aString.TakeWhile(c => c != '-');  
  
        // Execute the second query  
        foreach (char c in stringQuery2)  
            Console.Write(c);  
  
        Console.WriteLine(System.Environment.NewLine + "Press any key to exit");  
        Console.ReadKey();  
    }  
}  
/* Output:  
  Output: 9 9 7 4 1 2 8 9  
  Count = 8  
  ABCDE99F  
*/

Compiling the Code

Create a C# console application project, with using directives for the System.Linq and System.IO namespaces.

See also