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

Applies a key-generating function to each element of a sequence and returns a sequence that contains the elements of the original sequence as well its key and index inside the group of its key. An additional parameter specifies a comparer to use for testing the equivalence of keys.

Definition

Namespace: MoreLinq
Assembly: MoreLinq (in MoreLinq.dll) Version: 4.1.0+0e154ef592f33ce0f6f3d534a9eedee273f0ce72

C#

public static IEnumerable<KeyValuePair<int, TSource>> IndexBy<TSource, TKey>(
	this IEnumerable<TSource> source,
	Func<TSource, TKey> keySelector,
	IEqualityComparer<TKey>? comparer
)

VB

<ExtensionAttribute>
Public Shared Function IndexBy(Of TSource, TKey) ( 
	source As IEnumerable(Of TSource),
	keySelector As Func(Of TSource, TKey),
	comparer As IEqualityComparer(Of TKey)
) As IEnumerable(Of KeyValuePair(Of Integer, TSource))

C++

public:
[ExtensionAttribute]
generic<typename TSource, typename TKey>
static IEnumerable<KeyValuePair<int, TSource>>^ IndexBy(
	IEnumerable<TSource>^ source, 
	Func<TSource, TKey>^ keySelector, 
	IEqualityComparer<TKey>^ comparer
)

F#

[<ExtensionAttribute>]
static member IndexBy : 
        source : IEnumerable<'TSource> * 
        keySelector : Func<'TSource, 'TKey> * 
        comparer : IEqualityComparer<'TKey> -> IEnumerable<KeyValuePair<int, 'TSource>>

Parameters

source IEnumerableTSource: Source sequence.
keySelector FuncTSource, TKey: Function that projects the key given an element in the source sequence.
comparer 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: Type of the source sequence elements.
TKey: Type of the projected key.

Return Value

IEnumerableKeyValuePairInt32, TSource
A sequence of elements paired with their index within the key-group. The index is the key and the element is the value of the pair.

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).