ToDictionary(TSource, TKey, TElement) Method (IEnumerable(TSource), Func(TSource, TKey), Func(TSource, TElement), IEqualityComparer(TKey))

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

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

Type Parameters


The type of the elements of source.


The type of the key returned by keySelector.


The type of the value returned by elementSelector.


Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> to create a Dictionary<TKey, TValue> from.
Type: System.Func<TSource, TKey>
A function to extract a key from each element.
Type: System.Func<TSource, TElement>
A transform function to produce a result element value from each element.
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.


source or keySelector or elementSelector 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.


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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