Filtering Data
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'.
.png "LINQ Filtering Operation")
The standard query operator methods that perform selection are listed in the following section.
Methods
Method Name |
Description |
C# Query Expression Syntax |
Visual Basic Query Expression Syntax |
More Information |
|---|---|---|---|---|
OfType |
Selects values, depending on their ability to be cast to a specified type. |
Not applicable. |
Not applicable. |
|
Where |
Selects values that are based on a predicate function. |
where |
Where |
Query Expression Syntax Example
The following example uses the where clause in C# or the Where clause in Visual Basic to filter from an array those strings that have a specific length.
Dim words() As String = {"the", "quick", "brown", "fox", "jumps"}
Dim query = From word In words
Where word.Length = 3
Select word
Dim sb As New System.Text.StringBuilder()
For Each str As String In query
sb.AppendLine(str)
Next
' Display the results.
MsgBox(sb.ToString())
' This code produces the following output:
' the
' fox
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
Tasks
How to: Dynamically Specify Predicate Filters at Runtime (C# Programming Guide)
How to: Filter Query Results by Using LINQ (Visual Basic)
How to: Query An Assembly's Metadata with Reflection (LINQ)
How to: Query for Files with a Specified Attribute or Name
How to: Sort or Filter Text Data by Any Word or Field (LINQ)