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Filtering Data in C# with LINQ

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Filtering refers to the operation of restricting the result set to contain only those elements that satisfy a specified condition. It's also referred to as selecting elements that match the specified condition.

Important

These samples use an System.Collections.Generic.IEnumerable<T> data source. Data sources based on System.Linq.IQueryProvider use System.Linq.IQueryable<T> data sources and expression trees. Expression trees have limitations on the allowed C# syntax. Furthermore, each IQueryProvider data source, such as EF Core may impose more restrictions. Check the documentation for your data source.

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'.

Diagram that shows a LINQ filtering operation

The standard query operator methods that perform selection are listed in the following table:

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

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
*/

The equivalent query using method syntax is shown in the following code:

string[] words = ["the", "quick", "brown", "fox", "jumps"];

IEnumerable<string> query =
    words.Where(word => word.Length == 3);

foreach (string str in query)
{
    Console.WriteLine(str);
}

/* This code produces the following output:

    the
    fox
*/

See also