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    copied!<p>Ok, let's do some bounty hunting ;)</p> <p><strong>Step 0 - Sanitize example:</strong><br> As already mentioned, your example data is broken, as it does not define a valid nested set. If you took this data from an app, you should check the insert/delete logic.</p> <p>So for testing, I used a sanitized version like so:<br> (MySQL here, as it was the first at hand)</p> <pre><code>CREATE TABLE t_categories`( `id` INTEGER UNSIGNED NOT NULL AUTO_INCREMENT, `title` VARCHAR(45) NOT NULL, `lft` INTEGER UNSIGNED NOT NULL, `rght` INTEGER UNSIGNED NOT NULL, PRIMARY KEY (`id`) ); INSERT INTO t_categories (title, lft, rght) VALUES ('Cat 1',1,16); INSERT INTO t_categories (title, lft, rght) VALUES ('Cat 2',2,3); INSERT INTO t_categories (title, lft, rght) VALUES ('Cat 3',4,7); INSERT INTO t_categories (title, lft, rght) VALUES ('Cat 4',5,6); INSERT INTO t_categories (title, lft, rght) VALUES ('Cat 5',8,13); INSERT INTO t_categories (title, lft, rght) VALUES ('Cat 6',9,12); INSERT INTO t_categories (title, lft, rght) VALUES ('Cat 7',10,11); INSERT INTO t_categories (title, lft, rght) VALUES ('Cat 8',14,15); </code></pre> <p><strong>Step 1 - Let the database do the ordering</strong><br> Nested sets where primarily invented as a convenient way of storing trees in databases, as they make it pretty easy to query for subtrees, parent relations and, especially interesting in this case, for order and depth:</p> <pre><code>SELECT node.title, (COUNT(parent.title) - 1) AS depth FROM t_categories AS node CROSS JOIN t_categories AS parent WHERE node.lft BETWEEN parent.lft AND parent.rght GROUP BY node.title ORDER BY node.lft </code></pre> <p>This will return your set neatly ordered, starting with the root node and continuing to the end in preorder. Most importantly, it will add the depth of each node as a positive integer, indicating how many levels the node is below root (level 0). For the above example data, the result will be:</p> <pre><code>title, depth 'Cat 1', 0 'Cat 2', 1 'Cat 3', 1 'Cat 4', 2 'Cat 5', 1 'Cat 6', 2 'Cat 7', 3 'Cat 8', 1 </code></pre> <p>In code:</p> <pre><code>// Grab ordered data $query = ''; $query .= 'SELECT node.title, (COUNT(parent.title) - 1) AS depth'; $query .= ' FROM t_categories AS node'; $query .= ' CROSS JOIN t_categories AS parent'; $query .= ' WHERE node.lft BETWEEN parent.lft AND parent.rght'; $query .= ' GROUP BY node.title'; $query .= ' ORDER BY node.lft'; $result = mysql_query($query); // Build array $tree = array(); while ($row = mysql_fetch_assoc($result)) { $tree[] = $row; } </code></pre> <p>The resulting array will look like this:</p> <pre><code>Array ( [0] =&gt; Array ( [title] =&gt; Cat 1 [depth] =&gt; 0 ) [1] =&gt; Array ( [title] =&gt; Cat 2 [depth] =&gt; 1 ) ... ) </code></pre> <p><strong>Step 2 - Output as HTML list fragment:</strong> </p> <p>Using while loop:</p> <pre><code>// bootstrap loop $result = ''; $currDepth = -1; // -1 to get the outer &lt;ul&gt; while (!empty($tree)) { $currNode = array_shift($tree); // Level down? if ($currNode['depth'] &gt; $currDepth) { // Yes, open &lt;ul&gt; $result .= '&lt;ul&gt;'; } // Level up? if ($currNode['depth'] &lt; $currDepth) { // Yes, close n open &lt;ul&gt; $result .= str_repeat('&lt;/ul&gt;', $currDepth - $currNode['depth']); } // Always add node $result .= '&lt;li&gt;' . $currNode['title'] . '&lt;/li&gt;'; // Adjust current depth $currDepth = $currNode['depth']; // Are we finished? if (empty($tree)) { // Yes, close n open &lt;ul&gt; $result .= str_repeat('&lt;/ul&gt;', $currDepth + 1); } } print $result; </code></pre> <p>Same logic as recursive function:</p> <pre><code>function renderTree($tree, $currDepth = -1) { $currNode = array_shift($tree); $result = ''; // Going down? if ($currNode['depth'] &gt; $currDepth) { // Yes, prepend &lt;ul&gt; $result .= '&lt;ul&gt;'; } // Going up? if ($currNode['depth'] &lt; $currDepth) { // Yes, close n open &lt;ul&gt; $result .= str_repeat('&lt;/ul&gt;', $currDepth - $currNode['depth']); } // Always add the node $result .= '&lt;li&gt;' . $currNode['title'] . '&lt;/li&gt;'; // Anything left? if (!empty($tree)) { // Yes, recurse $result .= renderTree($tree, $currNode['depth']); } else { // No, close remaining &lt;ul&gt; $result .= str_repeat('&lt;/ul&gt;', $currNode['depth'] + 1); } return $result; } print renderTree($tree); </code></pre> <p>Both will output the following structure:</p> <pre><code>&lt;ul&gt; &lt;li&gt;Cat 1&lt;/li&gt; &lt;li&gt; &lt;ul&gt; &lt;li&gt;Cat 2&lt;/li&gt; &lt;li&gt;Cat 3&lt;/li&gt; &lt;li&gt; &lt;ul&gt; &lt;li&gt;Cat 4&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;li&gt;Cat 5&lt;/li&gt; &lt;li&gt; &lt;ul&gt; &lt;li&gt;Cat 6&lt;/li&gt; &lt;li&gt; &lt;ul&gt; &lt;li&gt;Cat 7&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;li&gt;Cat 8&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;/ul&gt; </code></pre> <hr> <p>Nitpickers corner: Questioner explicitly asked for <code>&lt;ul&gt;</code>, but <em>ordered</em> unordered lists!? Come on...<br> <strong>;-)</strong></p>
 

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