Linq extension method, how to find child in collection recursive

Question

I\'m already familiar with Linq but have little understanding of extension methods I\'m hoping someone can help me out.

So I have this hierarchical collection pseudo cod

Answer 1

An alternative solution using the yield to optimize the enumerations needed.

public static IEnumerable SelectManyRecursive(
    this IEnumerable source,
    Func> childrenSelector)
{
    if (source == null)
        throw new ArgumentNullException("source");

    foreach (var i in source)
    {
        yield return i;
        var children = childrenSelector(i);
        if (children != null)
        {
            foreach (var child in SelectManyRecursive(children, childrenSelector))
            {
                yield return child;
            }
        }
    }
}

Then you can find a match by calling something like FirstOrDefault:

    var match = People.SelectManyRecursive(c => c.Children)
                      .FirstOrDefault(x => x.Id == 5);