StackOverflow2013

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copied!<p>This code should do the trick</p> <pre><code>public static class Extensions { public static IEnumerable<T> GetRecursively<T>(this IEnumerable collection, Func<T, IEnumerable> selector) { foreach (var item in collection.OfType<T>()) { yield return item; IEnumerable<T> children = selector(item).GetRecursively(selector); foreach (var child in children) { yield return child; } } } } </code></pre> <p>Here's an example of how to use it</p> <pre><code>TreeView view = new TreeView(); // ... IEnumerable<TreeNode> nodes = view.Nodes. .GetRecursively<TreeNode>(item => item.Nodes); </code></pre> <p><strong>Update:</strong> In response to Eric Lippert's post.</p> <p>Here's a much improved version using the technique discussed in <a href="http://blogs.msdn.com/wesdyer/archive/2007/03/23/all-about-iterators.aspx" rel="nofollow noreferrer">All About Iterators</a>.</p> <pre><code>public static class Extensions { public static IEnumerable<T> GetItems<T>(this IEnumerable collection, Func<T, IEnumerable> selector) { Stack<IEnumerable<T>> stack = new Stack<IEnumerable<T>>(); stack.Push(collection.OfType<T>()); while (stack.Count > 0) { IEnumerable<T> items = stack.Pop(); foreach (var item in items) { yield return item; IEnumerable<T> children = selector(item).OfType<T>(); stack.Push(children); } } } } </code></pre> <p>I did a simple performance test using the following <a href="https://stackoverflow.com/questions/1507405/c-is-this-benchmarking-class-accurate">benchmarking technique</a>. The results speak for themselves. The depth of the tree has only marginal impact on the performance of the second solution; whereas the performance decreases rapidly for the first solution, eventually leadning to a <code>StackOverflowException</code> when the depth of the tree becomes too great.</p> <p><img src="https://i.stack.imgur.com/iI4JO.png" alt="benchmarking"></p>

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