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


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

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

public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey>(
	this IEnumerable<TSource> source,
	Func<TSource, TKey> keySelector,
	IEqualityComparer<TKey> comparer


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

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

Type: System.Func<TSourceTKey>

A function to extract a key from each element.

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

An IEqualityComparer<T> to compare keys.

Return Value

Type: System.Collections.Generic.Dictionary<TKeyTSource>

A Dictionary<TKey, TValue> that contains keys and values.

Type Parameters


The type of the elements of source.


The type of the keys returned by keySelector.

Exception Condition

source or keySelector is null.


keySelector produces a key that is null.


keySelector produces duplicate keys for two elements.

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

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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