Aggregation
Aggregate, Average, Count, LongCount, Max, Min, Sum
Conversion
AsEnumerable, Cast, OfType, ToArray, ToDictionary, ToList, ToLookup
Element
ElementAt, ElementAtOrDefault, First, FirstOrDefault, Last, LastOrDefault, Single, SingleOrDefault
ElementAt
ElementAtOrDefault
First (simple)
First (conditional)
FirstOrDefault
Last
LastOrDefault (simple)
LastOrDefault (conditional)
Single
SingleOrDefault
Generation
DefaultIfEmpty, Empty, Range, Repeat
Grouping
GroupBy
Join
GroupJoin, Join
Ordering
OrderBy, OrderByDescending, Reverse, ThenBy, ThenByDescending
OrderBy (simple - numbers)
OrderBy (simple - dates)
OrderBy (simple - objects)
OrderByDescending
Reverse
ThenBy
ThenByDescending
Other
Concat, SequenceEqual, Zip
Partitioning
Skip, SkipWhile, Take, TakeWhile
Projection
Select, SelectMany
Quantifiers
All, Any, Contains
Restriction
Where
Set
Distinct, Except, Intersect, Union
Close
Single: Retrieves only element in a collection. Throws exception if not exactly one element in collection.
| Single: Retrieves only element in a collection. Throws exception if not exactly one element in collection. |
| Single: Retrieves only element in a collection. Throws exception if not exactly one element in collection. |
| This Lambda Expression sample retrieves a single element from each array, but from arrays with not exactly one element it throws exception. |
| This Lambda Expression sample retrieves a single element from each array, but from arrays with not exactly one element it throws exception. |
// A Query Expression cannot be constructed for Single() in C#. // Consider using a Lambda Expression instead.
' A Query Expression cannot be constructed for Single() in VB.NET. ' Consider using a Lambda Expression instead.
// There is no Single() for Query Expressions in F#, but it has the similar "exactlyOne".
// Note: Single will throw an Exception, if there is not exactly one element in the array.
let Sample_Single_Linq() =
let names1 = [|"Peter" |]
let names3 = [|"Peter"; "Joe"; "Wilma"|]
let empty:System.Object list = []
let result1 = query {
for n in names1 do
exactlyOne
}
Debug.WriteLine(sprintf "The only name in the array is:")
Debug.WriteLine(sprintf "%s" result1)
try
// This will throw an exception because array contains no elements
let resultEmpty = query {
for e in empty do
exactlyOne
}
()
with
| ex -> Debug.WriteLine(sprintf "%s" ex.Message)
try
// This will throw an exception as well because array contains more than one element
let result3 = query {
for n in names3 do
exactlyOne
}
()
with
| ex -> Debug.WriteLine(sprintf "%s" ex.Message)
Output: The only name in the array is: Peter A first chance exception of type 'System.InvalidOperationException' occurred in System.Core.dll Sequence contains no elements A first chance exception of type 'System.InvalidOperationException' occurred in System.Core.dll Sequence contains more than one element
// Note: Single will throw an Exception, if there is not exactly one element in the array.
static void Sample_Single_Lambda()
{
string[] names1 = { "Peter" };
string[] names3 = { "Peter", "Joe", "Wilma" };
string[] empty = { };
var result1 = names1.Single();
Debug.WriteLine("The only name in the array is:");
Debug.WriteLine(result1);
try
{
// This will throw an exception because array contains no elements
var resultEmpty = empty.Single();
}
catch (Exception e)
{
Debug.WriteLine(e.Message);
}
try
{
// This will throw an exception as well because array contains more than one element
var result3 = names3.Single();
}
catch (Exception e)
{
Debug.WriteLine(e.Message);
}
}
Output: The only name in the array is: Peter A first chance exception of type 'System.InvalidOperationException' occurred in System.Core.dll Sequence contains no elements A first chance exception of type 'System.InvalidOperationException' occurred in System.Core.dll Sequence contains more than one element
' Note: Single will throw an Exception, if there is not exactly one element in the array.
Private Shared Sub Sample_Single_Lambda()
Dim names1 As String() = {"Peter"}
Dim names3 As String() = {"Peter", "Joe", "Wilma"}
Dim empty As String() = {}
Dim result1 = names1.Single()
Debug.WriteLine("The only name in the array is:")
Debug.WriteLine(result1)
Try
' This will throw an exception because array contains no elements
Dim resultEmpty = empty.Single()
Catch e As Exception
Debug.WriteLine(e.Message)
End Try
Try
' This will throw an exception as well because array contains more than one element
Dim result3 = names3.Single()
Catch e As Exception
Debug.WriteLine(e.Message)
End Try
End Sub
Output: The only name in the array is: Peter A first chance exception of type 'System.InvalidOperationException' occurred in System.Core.dll Sequence contains no elements A first chance exception of type 'System.InvalidOperationException' occurred in System.Core.dll Sequence contains more than one element
// Note: Single will throw an Exception, if there is not exactly one element in the array.
let Sample_Single_Lambda() =
let names1 = [|"Peter" |]
let names3 = [|"Peter"; "Joe"; "Wilma"|]
let empty = [| |]
let result1 = names1.Single()
Debug.WriteLine(sprintf "The only name in the array is:")
Debug.WriteLine(sprintf "%s" result1)
try
// This will throw an exception because array contains no elements
let resultEmpty = empty.Single()
()
with
| ex -> Debug.WriteLine(sprintf "%s" ex.Message)
try
// This will throw an exception as well because array contains more than one element
let result3 = names3.Single()
()
with
| ex -> Debug.WriteLine(sprintf "%s" ex.Message)
Output: The only name in the array is: Peter A first chance exception of type 'System.InvalidOperationException' occurred in System.Core.dll Sequence contains no elements A first chance exception of type 'System.InvalidOperationException' occurred in System.Core.dll Sequence contains more than one element