How can I add an element to an IEnumerable in C#

Question

I have the following code:

      var contentTypes =
          (
              from contentType in this._contentTypeService.GetContentTypes()
              select new
              {
                  id = contentType.ContentTypeId,
                  name = contentType.Name
              }
          );

How can I add another element to contentTypes with an id of 99 and a name of "All"?

I was trying to use contentTypes.Add(

but that does not seem to be allowed with intellisense.

You can convert contentTypes to List and then invoke Add method on it. — Suresh, Jun 21 '13 at 16:06
Gemma, you should check for existing Q&A before posting a new question. This has been asked multiple times on StackOverflow, using virtually the same title you used for your question. — Judah Gabriel Himango, Jun 21 '13 at 16:08

score 2 · Answer 1 · answered Jun 21 '13 at 16:09

You can't add to an IEnumerable<T>. IEnumerable<T>s represent sequences that you can iterate over; they do not represent a collection that you can add to. What you can do is concatenate to the end of your sequence though, obtaining a new sequence:

var sequence = contentTypes.Concat(
                   new[] {
                       new { id = 99, name = "All" }
                   }
               );

Now, if you iterate over sequence, you'll first see the elements of contentTypes streamed to you, and then the final item will be the appended item new { id = 99, name = "All" }.

score 1 · Answer 2 · answered Jun 21 '13 at 16:13

You can concatenate your new values to the end of the IEnumerable<>.

var contentTypes =
   (
      from contentType in new[]{new {ContentTypeId = 1, Name="TEST"}}
      select new
      {
          id = contentType.ContentTypeId,
          name = contentType.Name
      }
   ).Concat(new[]{new {id = 99, name="All"}});

The resulting IEnumerable will end with 99/All

score 0 · Answer 3 · answered Jun 21 '13 at 16:06

0

If you use contentTypes.ToList() you can then add to that list, however doing so will create a new instance of a collection, so your not actually modifying the source collection.

answered Jun 21 '13 at 16:06

Jay

6,224
4
20
23

score 0 · Answer 4 · answered Jun 21 '13 at 16:07

Try this -

var contentTypes =
          (
              from contentType in this._contentTypeService.GetContentTypes()
              select new
              {
                  id = contentType.ContentTypeId,
                  name = contentType.Name
              }
          ).ToList();

As you have converted contentTypes to a List, it should allow you to add a new item to it.

Tim Schmelter · Answer 5 · 2013-06-21T16:18:31.850

First, you cannot use IList.Add on an IEnumerable<T>. So you need to create a new collection.

You are selecting an anonymous type, use Concat to add a fixed anynymous type to your query:

var allTypes = new[]{new { id = 99, name = "All" }};    // creates a fixed anonymous type as `IEnumerable<T>`
var contentTypes = from contentType in this._contentTypeService.GetContentTypes()
                   select new
                   {
                       id = contentType.ContentTypeId,
                       name = contentType.Name
                   };
var result = allTypes.Concat(contentTypes).ToList(); // concat

How can I add an element to an IEnumerable in C#

5 Answers5