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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 
Thank you!
Tarek Elqusi wrote:
It would be nice if you supplied us with an example of the how to implement this idea with the c# collections such as the system.Windows.Forms.Control.ControlCollection as you mentioned

Then, you can use:
IEnumerable<Control> controlCollection = this.Controls.Cast<Control>();
In some cases, my signature will be longer then my message...
<em style="color:red">ProgramFOX</em>

Questiongood PinmemberUllasN22-Dec-12 20:23 
AnswerRe: good PinmemberProgramFOX22-Dec-12 21:46 
GeneralRe: good PinmemberUllasN22-Dec-12 23:12 

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