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Enumerable::ToDictionary<TSource, TKey, TElement> Method (IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, IEqualityComparer<TKey>)

Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function, a comparer, and an element selector function.

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

[ExtensionAttribute]
public:
generic<typename TSource, typename TKey, typename TElement>
static Dictionary<TKey, TElement>^ ToDictionary(
	IEnumerable<TSource>^ source, 
	Func<TSource, TKey>^ keySelector, 
	Func<TSource, TElement>^ elementSelector, 
	IEqualityComparer<TKey>^ comparer
)

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

TElement

The type of the value returned by elementSelector.

Parameters

source
Type: System.Collections.Generic::IEnumerable<TSource>

An IEnumerable<T> to create a Dictionary<TKey, TValue> from.

keySelector
Type: System::Func<TSource, TKey>

A function to extract a key from each element.

elementSelector
Type: System::Func<TSource, TElement>

A transform function to produce a result element value from each element.

comparer
Type: System.Collections.Generic::IEqualityComparer<TKey>

An IEqualityComparer<T> to compare keys.

Return Value

Type: System.Collections.Generic::Dictionary<TKey, TElement>
A Dictionary<TKey, TValue> that contains values of type TElement selected from the input sequence.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. 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).

ExceptionCondition
ArgumentNullException

source or keySelector or elementSelector is nullptr.

-or-

keySelector produces a key that is nullptr.

ArgumentException

keySelector produces duplicate keys for two elements.

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

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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