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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'.

LINQ Filtering Operation

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

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.

Enumerable.OfType<TResult>

Queryable.OfType<TResult>

Where

Selects values that are based on a predicate function.

where

Where

Enumerable.Where

Queryable.Where

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.


            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
            */
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