System.Linq.Enumerable.Single()

Returns the single element of a sequence, and throws an exception if there is not exactly one element in the sequence.

Syntax

public static TSource Single<TSource>(this IEnumerable<TSource> source);

Parameters

Name	Type	Description
`source`	`IEnumerable<TSource>`	An `IEnumerable<TSource>` that contains the elements to return a single element from.

Type Parameters

Name	Description
`TSource`	The type of the elements of `source`.

Return Value

TSource

The single element of type TSource in the input sequence.

Exceptions

ArgumentNullException: source is null.
InvalidOperationException: The input sequence is empty or contains more than one element.

Examples

Example 1: Getting the single element from a sequence with one element

// Sample code
var numbers = new List<int> { 5 };
var singleNumber = numbers.Single(); // singleNumber will be 5

Example 2: Attempting to get the single element from an empty sequence (throws InvalidOperationException)

// Sample code
var emptyList = new List<int>();
try
{
    var result = emptyList.Single();
}
catch (InvalidOperationException ex)
{
    // The exception message will indicate that the sequence is empty.
    Console.WriteLine(ex.Message);
}

Example 3: Attempting to get the single element from a sequence with multiple elements (throws InvalidOperationException)

// Sample code
var multipleNumbers = new List<int> { 1, 2, 3 };
try
{
    var result = multipleNumbers.Single();
}
catch (InvalidOperationException ex)
{
    // The exception message will indicate that the sequence contains more than one element.
    Console.WriteLine(ex.Message);
}

The Single() method is useful when you expect a sequence to contain exactly one item. If the sequence contains zero or more than one item, it throws an InvalidOperationException, which helps you catch unexpected data scenarios.