Enumerable.Single<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)

Type Parameters

• TSource
  The type of the elements of source.

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: TSource
The single element of the input sequence that satisfies a condition.

' Create an array of strings.
Dim fruits() As String = _
    {"apple", "banana", "mango", "orange", "passionfruit", "grape"}

' Get the single item in the array whose length is greater than 10.
Dim result As String = _
    fruits.Single(Function(fruit) fruit.Length > 10)

' Display the result.
outputBlock.Text &= "First query: " & result & vbCrLf

      string[] fruits = { "apple", "banana", "mango", 
                               "orange", "passionfruit", "grape" };

      string fruit1 = fruits.Single(fruit => fruit.Length > 10);

      outputBlock.Text += fruit1 + "\n";

      /*
       This code produces the following output:

       passionfruit
      */

      result = String.Empty

      ' Try to get the single item in the array whose length is > 15.
      Try
         result = fruits.Single(Function(fruit) _
                                    fruit.Length > 15)
      Catch ex As System.InvalidOperationException
         result = "There is not EXACTLY ONE element whose length is > 15."
      End Try

      ' Display the result.
      outputBlock.Text &= "Second query: " & result & vbCrLf

      ' This code produces the following output:
      '
      ' First query: passionfruit
      ' Second query: There is not EXACTLY ONE element whose length is > 15.

      string fruit2 = null;

      try
      {
         fruit2 = fruits.Single(fruit => fruit.Length > 15);
      }
      catch (System.InvalidOperationException)
      {
         outputBlock.Text += @"The collection does not contain exactly 
                             one element whose length is greater than 15." + "\n";
      }

      outputBlock.Text += fruit2 + "\n";

      // This code produces the following output:
      //
      // The collection does not contain exactly  
      // one element whose length is greater than 15.