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

Okay here's another version which is combined from about 3 answers above.

Recursive. Uses yield. Generic. Optional filter predicate. Optional selection function. About as concise as I could make it.

    public static IEnumerable Flatten(
        this IEnumerable nodes, 
        Func filterBy = null,
        Func> selectChildren = null
        )
    {
        if (nodes == null) yield break;
        if (filterBy != null) nodes = nodes.Where(filterBy);

        foreach (var node in nodes)
        {
            yield return node;

            var children = (selectChildren == null)
                ? node as IEnumerable
                : selectChildren(node);

            if (children == null) continue;

            foreach (var child in children.Flatten(filterBy, selectChildren))
            {
                yield return child;
            }
        }
    }

Usage:

// With filter predicate, with selection function
var flatList = nodes.Flatten(n => n.IsDeleted == false, n => n.Children);