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POHow to convert this MPTT array into a tree structure in PHP?
 

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  1. POHow to convert this MPTT array into a tree structure in PHP?
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    <p>I've got hierarchal data in the database, stored in <a href="http://www.sitepoint.com/article/hierarchical-data-database/" rel="nofollow noreferrer">Modified Preorder Tree Traversal</a> format. I'm pulling the data in a query that looks something like "SELECT ID, <code>Left</code>, <code>Right</code>, Name, etc FROM Table ORDER BY <code>Left</code>;". I'm trying to convert this data from a flat array the DB gives me into a tree-structure which I will then output as JSON with PHP's json_encode function.</p> <p>I'm having trouble getting my tree structure code to work beyond the first level, though. Here's a minimum test case:</p> <pre><code>&lt;pre&gt;&lt;?php function projectListToTree($projects) { $stack = Array(); for($x =0; $x &lt; count($projects); $x++) { $project = $projects[$x]; $project['Children'] = Array(); while(count($stack) &gt; 0 &amp;&amp; $stack[count($stack) - 1]['Right'] &lt; $project['Right']) { array_pop($stack); } if(count($stack) &gt; 0) { $stack[count($stack) - 1]['Children'][] = $project; echo "Adding " . $project['Name'] . " to " . $stack[count($stack) - 1]['Name'] . " for a total of " . count($stack[count($stack) - 1]['Children']) . " kids\n"; } else { echo "No parent\n"; } echo "stack count: " . count($stack) . "\n"; array_push($stack, $project); } echo "Left in stack: " . count($stack) . "\n"; return $stack[0]; } /* This is basically what comes from the DB. Should be: Parent First Child Second Child Grand Child */ $projects = Array( Array( "ID" =&gt; "2", "Left" =&gt; "2", "Right" =&gt; "9", "ParentID" =&gt; "1", "Name" =&gt; "Parent" ), Array( "ID" =&gt; "3", "Left" =&gt; "3", "Right" =&gt; "4", "ParentID" =&gt; "2", "Name" =&gt; "First Child" ), Array( "ID" =&gt; "4", "Left" =&gt; "5", "Right" =&gt; "8", "ParentID" =&gt; "2", "Name" =&gt; "Second Child" ), Array( "ID" =&gt; "5", "Left" =&gt; "6", "Right" =&gt; "7", "ParentID" =&gt; "4", "Name" =&gt; "Grand Child" ) ); $tree = projectListToTree($projects); echo "-----\n\n\n\n"; var_dump($tree); ?&gt;&lt;/pre&gt; </code></pre> <p>And here's what I'm getting for output:</p> <pre><code>No parent stack count: 0 Adding First Child to Parent for a total of 1 kids stack count: 1 Adding Second Child to Parent for a total of 2 kids stack count: 1 Adding Grand Child to Second Child for a total of 1 kids stack count: 2 Left in stack: 3 ----- array(6) { ["ID"]=&gt; string(1) "2" ["Left"]=&gt; string(1) "2" ["Right"]=&gt; string(1) "9" ["ParentID"]=&gt; string(1) "1" ["Name"]=&gt; string(6) "Parent" ["Children"]=&gt; array(2) { [0]=&gt; array(6) { ["ID"]=&gt; string(1) "3" ["Left"]=&gt; string(1) "3" ["Right"]=&gt; string(1) "4" ["ParentID"]=&gt; string(1) "2" ["Name"]=&gt; string(11) "First Child" ["Children"]=&gt; array(0) { } } [1]=&gt; array(6) { ["ID"]=&gt; string(1) "4" ["Left"]=&gt; string(1) "5" ["Right"]=&gt; string(1) "8" ["ParentID"]=&gt; string(1) "2" ["Name"]=&gt; string(12) "Second Child" ["Children"]=&gt; array(0) { } } } } </code></pre> <p>As you can see, somewhere "Grandchild" is getting lost, even though the output in the projectListToTree function seems to indicate it should be there. It seems like any tree structure I throw at it drops anything below the second level. Any insight into what might be happening?</p> <p>Thanks!</p>
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