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)
static member Single<'TSource> : source:IEnumerable<'TSource> * predicate:Func<'TSource, bool> -> 'TSource
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.
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.
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