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

July 28, 2014

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 Parameters

TSource

The type of the elements of source.

TKey

The type of the keys returned by keySelector.

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.
comparer
Type: System.Collections.Generic.IEqualityComparer<TKey>
An IEqualityComparer<T> to compare keys.

Return Value

Type: System.Collections.Generic.Dictionary<TKey, TSource>
A Dictionary<TKey, TValue> that contains keys and values.

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.

ExceptionCondition
ArgumentNullException

source or keySelector is null.

-or-

keySelector produces a key that is null.

ArgumentException

keySelector produces duplicate keys for two elements.

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

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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