Recursive List Flattening

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 oth

Answer 1

Hmm... I'm not sure exactly what you want here, but here's a "one level" option:

public static IEnumerable Flatten (this IEnumerable sequences)
    where TSequence : IEnumerable 
{
    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?