How to Create an Echo Menu Tree Using a Recursive Function in PHP?

Echo Menu Tree with Recursive Function

Problem Overview

Creating a recursive function to traverse a hierarchical menu structure stored in a database and output it in HTML can be challenging. Given a table with categories and their parent categories, the task is to generate a menu tree that visually represents the hierarchy.

Recursive Function Approach

To solve this problem, a recursive function is needed. The idea is to start with the root category, find its children, and recursively call the function on each child, building up the HTML output as we go.

PHP Function Implementation

Here is a possible implementation of the PHP function:

<code class="php">function recurse($categories, $parent = null, $level = 0)
{
    $ret = '&lt;ul&gt;';
    foreach($categories as $index =&gt; $category)
    {
        if($category['root'] == $parent)
        {
            $ret .= '&lt;li&gt;&lt;a href=&quot;#&quot;&gt;&lt;p class=&quot;Tier' . $level . '&quot;&gt;' . $category['name'] . '&lt;/p&gt;&lt;/a&gt;';
            $ret .= $this-&gt;recurse($categories, $category['id'], $level+1);
            $ret .= '&lt;/li&gt;';
        }
    }
    return $ret . '&lt;/ul&gt;';
}</code>

1. It takes three parameters: $categories (an array of category data), $parent (the current parent category ID), and $level (which determines the level of indentation).
2. It iterates through the categories and checks if their root matches the provided parent ID.
3. If there is a match, it output the category name, wrapped in an li and a element with an appropriate Tier class for indentation.
4. It then recursively calls itself with the next level of categories, setting the new parent ID and incrementing the level.

Usage

To use the function:

1. Query the database to retrieve all categories.
2. Call recurse() with the category data as the first parameter.
3. Echo the returned HTML output.

Handling Empty Child Categories

The initial implementation may produce empty <ul> elements for categories with no children. To prevent this, you can modify the function like so:

<code class="php">function recurse($categories, $parent = null, $level = 0)
{
    $ret = '&lt;ul&gt;';
    foreach($categories as $index =&gt; $category)
    {
        if($category['root'] == $parent)
        {
            $ret .= '&lt;li&gt;&lt;a href=&quot;#&quot;&gt;&lt;p class=&quot;Tier' . $level . '&quot;&gt;' . $category['name'] . '&lt;/p&gt;&lt;/a&gt;';
            $sub = $this-&gt;recurse($categories, $category['id'], $level+1);
            if($sub != '&lt;ul&gt;&lt;/ul&gt;')
                $ret .= $sub;
            $ret .= '&lt;/li&gt;';
        }
    }
    return $ret . '&lt;/ul&gt;';
}</code>

This modification ensures that only categories with children have <ul> elements.

Alternatively, you can add a child count to each category and only include the <ul> if the child count is greater than zero.

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