Enumerable.Single<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)
Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists.
Assembly: System.Core (in System.Core.dll)
public static TSource Single<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate )
Parameters
- source
-
Type:
System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> to return a single element from.
- predicate
-
Type:
System.Func<TSource, Boolean>
A function to test an element for a condition.
Return Value
Type: TSourceThe single element of the input sequence that satisfies a condition.
Type Parameters
- TSource
The type of the elements of source.
| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate is null. |
| InvalidOperationException | No element satisfies the condition in predicate. -or- More than one element satisfies the condition in predicate. -or- The source sequence is empty. |
The Single<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) method throws an exception if the input sequence contains no matching element. To instead return null when no matching element is found, use SingleOrDefault<TSource>.
The following code example demonstrates how to use Single<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) to select the only element of an array that satisfies a condition.
string[] fruits = { "apple", "banana", "mango", "orange", "passionfruit", "grape" }; string fruit1 = fruits.Single(fruit => fruit.Length > 10); Console.WriteLine(fruit1); /* This code produces the following output: passionfruit */
The following code example demonstrates that Single<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) throws an exception when the sequence does not contain exactly one element that satisfies the condition.
string fruit2 = null; try { fruit2 = fruits.Single(fruit => fruit.Length > 15); } catch (System.InvalidOperationException) { Console.WriteLine(@"The collection does not contain exactly one element whose length is greater than 15."); } Console.WriteLine(fruit2); // This code produces the following output: // // The collection does not contain exactly // one element whose length is greater than 15.
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1