How Can I Construct a Tree Data Structure from a Flat Array in PHP?

Build a Tree from an Array in PHP

Creating a tree data structure from a flat array can be a common task in programming. Suppose you have an array of elements, each with an 'id' and 'parent_id' field. Each element can have only one parent but may have multiple children. The goal is to transform this array into a tree structure to facilitate efficient navigation and retrieval of data.

Solution:

To build the tree, we can use a recursive function that iterates through the array and groups elements based on their parent-child relationships. The function takes two parameters: an array of elements and the ID of the parent node for the current level of the tree.

Here is a sample implementation:

function buildTree(array &$elements, $parentId = 0) {
    $branch = []; // Initialize an empty branch for this level

    foreach ($elements as $id => $element) { // Loop through each element
        if ($element['parent_id'] == $parentId) { // If the element's parent ID matches the current parent ID
            $children = buildTree($elements, $element['id']); // Recursively build the tree for the element's children
            $branch[$id] = $element; // Add the element to the current branch
            if ($children) { // If the element has children
                $branch[$id]['children'] = $children; // Add the children to the element
            }
            unset($elements[$id]); // Remove the processed element from the original array to avoid duplicates
        }
    }

    return $branch;
}

Using this function, you can transform a flat array of elements into a tree data structure efficiently. The resulting tree can be used for various purposes, such as managing hierarchical data, navigation menus, or organizational structures.

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