Windows apps
Collapse the table of content
Expand the table of content
The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

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

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)

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

Type Parameters


The type of the elements of source.


The type of the key returned by keySelector.


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.

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 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.

      class Package
         public string Company { get; set; }
         public double Weight { get; set; }
         public long TrackingNumber { get; set; }

      public static void ToDictionaryEx1()
         List<Package> packages =
             new List<Package>
                     { new Package { Company = "Coho Vineyard", Weight = 25.2, TrackingNumber = 89453312L },
                       new Package { Company = "Lucerne Publishing", Weight = 18.7, TrackingNumber = 89112755L },
                       new Package { Company = "Wingtip Toys", Weight = 6.0, TrackingNumber = 299456122L },
                       new Package { Company = "Adventure Works", Weight = 33.8, TrackingNumber = 4665518773L } };

         // Create a Dictionary of Package objects, 
         // using TrackingNumber as the key.
         Dictionary<long, Package> dictionary =
             packages.ToDictionary(p => p.TrackingNumber);

         foreach (KeyValuePair<long, Package> kvp in dictionary)
            outputBlock.Text += String.Format(
                "Key {0}: {1}, {2} pounds",
                kvp.Value.Weight) + "\n";

       This code produces the following output:

       Key 89453312: Coho Vineyard, 25.2 pounds
       Key 89112755: Lucerne Publishing, 18.7 pounds
       Key 299456122: Wingtip Toys, 6 pounds
       Key 4665518773: Adventure Works, 33.8 pounds


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.

Community Additions

© 2016 Microsoft