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Cast an IEnumerable to an IEnumerable(T)

By , 22 Dec 2012
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It's possible to use LINQ queries to get data from an IEnumerable<T>. But for an IEnumerable, you can't use LINQ. If you write this LINQ query for an IEnumerable:

IEnumerable ienumerable = new int[] { 1, 5, 6, 7, 8, 11, 10, 134, 90 };
var integer = from i in ienumerable where i > 10 select i;

Then, you get this error:

Could not find an implementation of the query pattern for 
source type 'System.Collections.IEnumerable'. 'Where' not found. 
Consider explicitly specifying the type of the range variable 'i'. 

In this tip, I tell you how to cast an IEnumerable to an IEnumerable<T>.

Cast an IEnumerable to an IEnumerable<T>

To cast an IEnumerable to an IEnumerable<T>, you can use this code:

IEnumerable ienumerable = new int[] { 1, 5, 6, 7, 8, 11, 10, 134, 90 };
IEnumerable casted = ienumerable.Cast<int>(); // change 'int' into the 
                              //type of the elements in your IEnumerable

Now, you can use a LINQ query for casted. But, an IEnumerable can contain different types:

IEnumerable ienumerable = new object[] { 1, 5, 6, 7, 8, 11, 10, 134, 90, "test" };

With this code, you can get all integers from the IEnumerable into a IEnumerable<T> using the OfType<T> function:

IEnumerable ienumerable = new object[] { 1, 5, 6, 7, 8, 11, 10, 134, 90, "test" };
IEnumerable<int> allIntegers = ienumerable.OfType<int>(); // change 'int' 
      // in the type of the elements you want to get from the IEnumerable

Points of Interest

There're many collection classes in C# that inherit from IEnumerable, for example System.Windows.Forms.Control.ControlCollection, System.Windows.Forms.HtmlElementCollection or System.Xml.XmlNodeList class. It's useful to use LINQ for these classes.


  • 22 Dec 2012: First version


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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Comments and Discussions

GeneralMy vote of 5 PinmemberTarek Elqusi23-Dec-12 5:27 
GeneralRe: My vote of 5 PinmemberProgramFOX23-Dec-12 22:51 
Questiongood PinmemberUllasN22-Dec-12 20:23 
AnswerRe: good PinmemberProgramFOX22-Dec-12 21:46 
GeneralRe: good PinmemberUllasN22-Dec-12 23:12 
Please keep posting small articles . Probably too much to ask of anyone but these small articles are the best as they are like little gems of knowledge that can read right off an RSS feed in a mobile device . Quick knowledge on the go keeps the brain ticking.

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