EnumerableToLookup Method
 
System_CAPS_noteNote

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Creates a Lookup from an IEnumerable according to a specified key selector function and key comparer.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

public static ILookup<TKey, TSource> ToLookup<TSource, TKey>(
	this IEnumerable<TSource> source,
	Func<TSource, TKey> keySelector,
	IEqualityComparer<TKey> comparer
)
public:
generic<typename TSource, typename TKey>
[ExtensionAttribute]
static ILookup<TKey, TSource>^ ToLookup(
	IEnumerable<TSource>^ source,
	Func<TSource, TKey>^ keySelector,
	IEqualityComparer<TKey>^ comparer
)
static member ToLookup<'TSource, 'TKey> : 
        source:IEnumerable<'TSource> *
        keySelector:Func<'TSource, 'TKey> *
        comparer:IEqualityComparer<'TKey> -> ILookup<'TKey, 'TSource>
<ExtensionAttribute>
Public Shared Function ToLookup(Of TSource, TKey) (
	source As IEnumerable(Of TSource),
	keySelector As Func(Of TSource, TKey),
	comparer As IEqualityComparer(Of TKey)
) As ILookup(Of TKey, TSource)

Parameters

source
Type:

The IEnumerable to create a Lookup from.

keySelector
Type:

A function to extract a key from each element.

comparer
Type:

An IEqualityComparer to compare keys.

Return Value

Type:

A Lookup that contains keys and values.

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

Exception Condition
ArgumentNullException

source or keySelector is null.

The ToLookup method returns a Lookup, a one-to-many dictionary that maps keys to collections of values. A Lookup is different to a Dictionary, which performs a one-to-one mapping of keys to single values.

If comparer is null, the default equality comparer is used to compare keys.

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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