Question

I could probably write this myself, but the specific way I’m trying to accomplish it is throwing me off. I’m trying to write a generic extension method similar to the others introduced in .NET 3.5 that will take a nested IEnumerable of IEnumerables (and so on) and flatten it into one IEnumerable. Anyone have any ideas?

Specifically, I’m having trouble with the syntax of the extension method itself so that I can work on a flattening algorithm.

Answer 1

Hmm… I’m not sure exactly what you want here, but here’s a ‘one level’ option:

public static IEnumerable<TElement> Flatten<TElement,TSequence> (this IEnumerable<TSequence> sequences)     where TSequence : IEnumerable<TElement>  {     foreach (TSequence sequence in sequences)     {         foreach(TElement element in sequence)         {             yield return element;         }     } } 

If that’s not what you want, could you provide the signature of what you do want? If you don’t need a generic form, and you just want to do the kind of thing that LINQ to XML constructors do, that’s reasonably simple – although the recursive use of iterator blocks is relatively inefficient. Something like:

static IEnumerable Flatten(params object[] objects) {     // Can't easily get varargs behaviour with IEnumerable     return Flatten((IEnumerable) objects); }  static IEnumerable Flatten(IEnumerable enumerable) {     foreach (object element in enumerable)     {         IEnumerable candidate = element as IEnumerable;         if (candidate != null)         {             foreach (object nested in candidate)             {                 yield return nested;             }         }         else         {             yield return element;         }     } } 

Note that that will treat a string as a sequence of chars, however – you may want to special-case strings to be individual elements instead of flattening them, depending on your use case.

Does that help?