Filtering Data (C#)

Filtering refers to the operation of restricting the result set to contain only those elements that satisfy a specified condition. It is also known as selection.

The following illustration shows the results of filtering a sequence of characters. The predicate for the filtering operation specifies that the character must be 'A'.

The standard query operator methods that perform selection are listed in the following section.

Methods

Method Name	Description	C# Query Expression Syntax	More Information
OfType	Selects values, depending on their ability to be cast to a specified type.	Not applicable.	Enumerable.OfType Queryable.OfType
Where	Selects values that are based on a predicate function.	where	Enumerable.Where Queryable.Where

Query Expression Syntax Example

The following example uses the where clause to filter from an array those strings that have a specific length.

string[] words = { "the", "quick", "brown", "fox", "jumps" };  
  
IEnumerable<string> query = from word in words  
                            where word.Length == 3  
                            select word;  
  
foreach (string str in query)  
    Console.WriteLine(str);  
  
/* This code produces the following output:  
  
    the  
    fox  
*/  

See also

• System.Linq
• Standard Query Operators Overview (C#)
• where clause
• Dynamically specify predicate filters at run time
• How to query an assembly's metadata with Reflection (LINQ) (C#)
• How to query for files with a specified attribute or name (C#)
• How to sort or filter text data by any word or field (LINQ) (C#)