MoreEnumerableExceptByTSource, TKey(IEnumerableTSource, IEnumerableTSource, FuncTSource, TKey, IEqualityComparerTKey) Method

Returns the set of elements in the first sequence which aren't in the second sequence, according to a given key selector.

Definition

Namespace: MoreLinq
Assembly: MoreLinq (in MoreLinq.dll) Version: 3.4.0+b99a6a8cc504caf2d48372fe54a2f8116c59cd0c

C#

public static IEnumerable<TSource> ExceptBy<TSource, TKey>(
	this IEnumerable<TSource> first,
	IEnumerable<TSource> second,
	Func<TSource, TKey> keySelector,
	IEqualityComparer<TKey>? keyComparer
)

VB

<ExtensionAttribute>
Public Shared Function ExceptBy(Of TSource, TKey) ( 
	first As IEnumerable(Of TSource),
	second As IEnumerable(Of TSource),
	keySelector As Func(Of TSource, TKey),
	keyComparer As IEqualityComparer(Of TKey)
) As IEnumerable(Of TSource)

C++

public:
[ExtensionAttribute]
generic<typename TSource, typename TKey>
static IEnumerable<TSource>^ ExceptBy(
	IEnumerable<TSource>^ first, 
	IEnumerable<TSource>^ second, 
	Func<TSource, TKey>^ keySelector, 
	IEqualityComparer<TKey>^ keyComparer
)

F#

[<ExtensionAttribute>]
static member ExceptBy : 
        first : IEnumerable<'TSource> * 
        second : IEnumerable<'TSource> * 
        keySelector : Func<'TSource, 'TKey> * 
        keyComparer : IEqualityComparer<'TKey> -> IEnumerable<'TSource>

Parameters

first IEnumerableTSource: The sequence of potentially included elements.
second IEnumerableTSource: The sequence of elements whose keys may prevent elements in first from being returned.
keySelector FuncTSource, TKey: The mapping from source element to key.
keyComparer IEqualityComparerTKey: The equality comparer to use to determine whether or not keys are equal. If null, the default equality comparer for TSource is used.

Type Parameters

TSource: The type of the elements in the input sequences.
TKey: The type of the key returned by keySelector.

Return Value

IEnumerableTSource
A sequence of elements from first whose key was not also a key for any element in second.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerableTSource. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

Remarks

This is a set operation; if multiple elements in first have equal keys, only the first such element is returned. This operator uses deferred execution and streams the results, although a set of keys from second is immediately selected and retained.