How do I convert IEnumerable to a custom type in C#?

Question

I am using extension methods OrderBy and ThenBy to sort my custom collection on multiple fields. This sort does not effect the collection but instead returns and IEnumberable. I am unable to cast the IEnumerable result to my custom collection. Is there anyway to change the order of my collection or convert the IEnumerable result to my custom collection?

Answer 1

If your collection type implements IList<T> (to be able to Add() to it) you could write an extension method:

public static Extensions
{
    public static TColl ToTypedCollection<TColl, T>(this IEnumerable ien)
        where TColl : IList<T>, new()
    {
        TColl collection = new TColl();

        foreach (var item in ien)
        {
            collection.Add((T) item);
        }

        return collection;
    }
}

Answer 2

No there isn't. When you use the query operators, it doesn't use instances of the original collection to generate the enumeration. Rather, it uses private implementations (possibly anonymous, possibly not) to provide this functionality.

If you want it in your original collection, you should have a constructor on the type which takes an IEnumerable<T> (or whatever your collection stores, if it is specific) and then pass the query to the constructor.

You can then use this to create an extension method for IEnumerable<T> called To<YourCollectionType> which would take the IEnumerable<T> and then pass it to the constructor of your type and return that.

Answer 3

No. You could follow the pattern established by the ToList and ToDictionary extension methods - write a similar extension method to load up your own collection type from IEnumerable.