How to search Hierarchical Data with Linq

Question

I need to search a tree for data that could be anywhere in the tree. How can this be done with linq?

class Program
{
    static void Main(string[] args) {

         


        

Answer 1

I like Kenneth Bo Christensen's answer using stack, it works great, it is easy to read and it is fast (and doesn't use recursion). The only unpleasant thing is that it reverses the order of child items (because stack is FIFO). If sort order doesn't matter to you then it's ok. If it does, sorting can be achieved easily using selector(current).Reverse() in the foreach loop (the rest of the code is the same as in Kenneth's original post)...

public static IEnumerable<T> Flatten<T>(this T source, Func<T, IEnumerable<T>> selector)
{            
    var stack = new Stack<T>();
    stack.Push(source);
    while (stack.Count > 0)
    {
        var current = stack.Pop();
        yield return current;
        foreach (var child in selector(current).Reverse())
            stack.Push(child);
    }
}

Answer 2

I have tried two of the suggested codes and made the code a bit more clear:

    public static IEnumerable<T> Flatten1<T>(this T source, Func<T, IEnumerable<T>> selector)
    {
        return selector(source).SelectMany(c => Flatten1(c, selector)).Concat(new[] { source });
    }

    public static IEnumerable<T> Flatten2<T>(this T source, Func<T, IEnumerable<T>> selector)
    {            
        var stack = new Stack<T>();
        stack.Push(source);
        while (stack.Count > 0)
        {
            var current = stack.Pop();
            yield return current;
            foreach (var child in selector(current))
                stack.Push(child);
        }
    }

Flatten2() seems to be a little bit faster but its a close run.