How to Convert Parent-Child Relationships into Hierarchical Trees in PHP?

Converting Parent-Child Relationships into Hierarchical Trees

In programming, it can be necessary to convert a series of parent-child relationships into a hierarchical tree structure. This task can be accomplished in PHP using a recursive approach.

Example Data:

Consider the following set of parent-child relationships:

Child : Parent
H : G
F : G
G : D
E : D
A : E
B : C
C : E
D : NULL

Transforming into Hierarchical Tree:

To transform this data into a hierarchical tree structure, we create two PHP functions:

• parseTree($tree, $root): This function recursively parses the child-parent pairs and constructs the tree.
• printTree($tree): This function traverses the tree and prints it as an unordered list.

parseTree Function:

function parseTree($tree, $root = null) {
    $return = array();
    foreach($tree as $child => $parent) {
        if($parent == $root) {
            unset($tree[$child]);
            $return[] = array(
                'name' => $child,
                'children' => parseTree($tree, $child)
            );
        }
    }
    return empty($return) ? null : $return;    
}

printTree Function:

function printTree($tree) {
    if(!is_null($tree) && count($tree) > 0) {
        echo '<ul>';
        foreach($tree as $node) {
            echo '<li>' . $node['name'];
            printTree($node['children']);
            echo '</li>';
        }
        echo '</ul>';
    }
}

Usage:

To use these functions, first initialize the array of child-parent pairs. Then call parseTree with the array and printTree with the resulting tree:

$tree = array(
    'H' => 'G',
    'F' => 'G',
    'G' => 'D',
    'E' => 'D',
    'A' => 'E',
    'B' => 'C',
    'C' => 'E',
    'D' => null
);

$result = parseTree($tree);
printTree($result);

Result:

The output will be an unordered list representing the hierarchical tree:

<ul>
<li>D
<ul>
<li>G
<ul>
<li>H</li>
<li>F</li>
</ul>
</li>
<li>E
<ul>
<li>A</li>
<li>C
<ul>
<li>B</li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>

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