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POWhy is this code for iterating over the DOM stupid slow?
 

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  1. POWhy is this code for iterating over the DOM stupid slow?
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    <p>This is nested about 10 functions deep, so I'll just paste the relevant bits:</p> <p>This line is really slow:</p> <pre><code>var nodes = Filter_Chunk(Traverse(), chunks.First()); </code></pre> <p>Specifically, this chunk inside <code>Filter_Chunk</code> (pun not intended):</p> <pre><code>private static IEnumerable&lt;HtmlNode&gt; Filter_Chunk(IEnumerable&lt;HtmlNode&gt; nodes, string selectorChunk) { // ... string tagName = selectorChunk; foreach (var node in nodes) if (node.Name == tagName) yield return node; </code></pre> <p>There's nothing too complicated in there... so I'm thinking it must be the sheer number of nodes in <code>Traverse()</code> right?</p> <pre><code>public IEnumerable&lt;HtmlNode&gt; Traverse() { foreach (var node in _context) { yield return node; foreach (var child in Children().Traverse()) yield return child; } } public SharpQuery Children() { return new SharpQuery(_context.SelectMany(n =&gt; n.ChildNodes).Where(n =&gt; n.NodeType == HtmlNodeType.Element), this); } </code></pre> <p>I tried finding <code>&lt;h3&gt;</code> nodes on <a href="https://stackoverflow.com/questions/4138803/wheres-the-bug-in-this-tree-traversal-code">stackoverflow.com</a>. There shouldn't be more than a couple thousand nodes, should there? Why is this taking many minutes to complete?</p> <hr> <p>Actually, there's definitely a bug in here somewhere that is causing it to return more nodes than it should... <a href="https://stackoverflow.com/questions/4138803/wheres-the-bug-in-this-tree-traversal-code">I forked the question to address the issue</a></p>
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      1. POWhy is this code for iterating over the DOM stupid slow?
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    1. COpossible duplicate of [C# Performance of nested yield in a tree](http://stackoverflow.com/questions/1043050/c-performance-of-nested-yield-in-a-tree)
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      1. USJon Skeet
    2. COI can't give you any sort of specific answer, but I can point you to an interesting article on Joelonsoftware.com Down near the bottom Joel talks about the performance hit of using XML for large data sets. http://www.joelonsoftware.com/articles/fog0000000319.html
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      1. USJesse McCulloch
    3. COJust a guess: try to use a List<HtmlNode> instead of IEnumerable / yield and tell us if this helps. Reason for your problem might be the overhead of the state machine the compiler internally builds for indexers when using yield.
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      1. USDoc Brown
 

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