How to assign an ienumerable object to a list in C#

You can't - because the result isn't a list of strings.

You could convert it to a list of strings, e.g.

List<string> response = ExecuteRequest(uri)
                              .Select(d => new {d.Id, d.TotalViews }.ToString())
                              .ToList();

... but I doubt that's what you really want. You should ask yourself:

• Why did you originally declare response to be of type List<string>?
• What type do you really want?
• If you want a pair of Id / TotalViews as per the anonymous type, there are three options:
  • If you only need it to be strongly-typed within the method, you can stick with an anonymous type, and declare the variable with var
  • Otherwise... you could build your own type with Id and TotalViews properties...
  • ... or you could potentially use Tuple<,> if you're using .NET 4

Here's the version using an anonymous type:

// The compiler knows the type of response, but you can't express it in normal
// C#, because it's IEnumerable<X> where X is the anonymous type... which you
// can't specify the name of, because it's anonymous...
var response = ExecuteRequest(uri).Select(d => new {d.Id, d.TotalViews })
                                  .ToList();

You are trying to stuff an anonymous type made from d.Id and d.TotalViews into a list of strings.

Either create a string from both of these before calling ToList on the result, or create a containing class for these and make a list of those instead of a String.

public class TotalViewsPerId
{
  public int Id {get;set;}
  public int TotalViews {get;set;}
}

List<TotalViewsPerId> response = ExecuteRequest(uri)
                              .Select(d => new TotalViewsPerId{d.Id, d.TotalViews })
                              .ToList();

You have declared a list of string, but you are trying to assign a list of an anonymous type. You could choose one of these options:

• Change the declaration to match the type you are trying to assign (in this case, an anonymous type):

  var response = ExecuteRequest(uri).Select(d => new {d.Id, d.TotalViews }).ToList();
  

Note that you can't return an anonymous type from a method.

• Change the type that you are trying to assign to match the declaration (in this case, List<string>):

  response = ExecuteRequest(uri).Select(d =>
          string.Format("{0} {1}", d.Id, d.TotalViews)
      ).ToList();
  

• Change both. Maybe a Dictionary<int, int> would be better for your needs?