How to Efficiently Build a Tree Structure from a Flat Array in PHP?

Building a Tree Structure from a Flat Array in PHP

Converting a flat array into a hierarchical tree structure can be a useful task in various programming scenarios. In this article, we tackle the problem of constructing a tree from an array with elements representing nodes, where each node has an ID and a parent ID.

To achieve this conversion, we employ a recursive function called buildTree. This function traverses the array and gradually builds the tree structure. At each recursive call, it focuses on a specific parent node and collects all its child nodes into a subtree. Once all child nodes are added to the subtree, it recursively builds subtrees for the child nodes and attaches them to the parent node.

The following PHP code demonstrates the implementation of this tree-building algorithm:

function buildTree(array &$elements, $parentId = 0) {
    $branch = array();

    foreach ($elements as $element) {
        if ($element['parent_id'] == $parentId) {
            $children = buildTree($elements, $element['id']);
            if ($children) {
                $element['children'] = $children;
            }
            $branch[$element['id']] = $element;
            unset($elements[$element['id']]);
        }
    }

    return $branch;
}

In this function, we iterate over the array and examine each element's parent_id value. If it matches the $parentId parameter, it means we're currently dealing with a child node of $parentId. We then recursively build the child node's subtree by invoking the buildTree function again with its ID as the $parentId argument.

Once the subtree for the current child node is built, we add it to the $branch array along with the current element. To prevent duplicate entries, we also remove the current element from the original array using unset().

This process continues recursively until all elements have been assigned to the appropriate subtree. Finally, the function returns the $branch array, which represents the constructed tree.

By utilizing this recursive approach, you can efficiently convert your flat array into a hierarchical tree structure, enabling you to work with complex relationships between data elements in a structured and organized manner.

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