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


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Creates a Dictionary<'TKey, 'TValue> from an IEnumerable<'T> according to a specified key selector function.

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

static member ToDictionary<'TSource, 'TKey> : 
        source:IEnumerable<'TSource> *
        keySelector:Func<'TSource, 'TKey> -> Dictionary<'TKey, 'TSource>


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.

Return Value

Type: System.Collections.Generic.Dictionary<'TKey, 'TSource>

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

Type Parameters


The type of the elements of source.


The type of the key returned by keySelector.

Exception Condition

source or keySelector is null.


keySelector produces a key that is null.


keySelector produces duplicate keys for two elements.

The ToDictionary<'TSource, 'TKey>(IEnumerable<'TSource>, Func<'TSource, 'TKey>) method uses the default equality comparer Default to compare keys.

The following code example demonstrates how to use ToDictionary<'TSource, 'TKey>(IEnumerable<'TSource>, Func<'TSource, 'TKey>) to create a Dictionary<'TKey, 'TValue> by using a key selector.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 8
.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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