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.
Assembly: System.Core (in System.Core.dll)
public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey>( this IEnumerable<TSource> source, Func<TSource, TKey> 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.
Return Value
Type: System.Collections.Generic.Dictionary<TKey, TSource>A Dictionary<TKey, TValue> that contains keys and values.
Type Parameters
- TSource
The type of the elements of source.
- TKey
The type of the key returned by keySelector.
| Exception | Condition |
|---|---|
| ArgumentNullException | source or keySelector is null. -or- keySelector produces a key that is null. |
| ArgumentException | 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) { Console.WriteLine( "Key {0}: {1}, {2} pounds", kvp.Key, kvp.Value.Company, kvp.Value.Weight); } } /* 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 */
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1