Let’s talk about how to convert a two-dimensional array into a tree structure in PHP

With the continuous development of network applications, more and more websites and applications are developed using front-end and back-end separation. This separates the front-end code from the back-end code and requires communication through data interaction. In the process of data interaction, arrays are often used, especially two-dimensional arrays. So how to convert a two-dimensional array into a tree structure? This article will share how to convert a two-dimensional array into a tree in PHP.

1. What is a tree structure

Before introducing how to convert a two-dimensional array into a tree shape, let us first understand what a tree structure is. In computer science, a tree structure is a nonlinear data structure, which is a set of hierarchical relationships composed of n (n>0) limited nodes. One of the nodes is called the root node, and the remaining nodes can be viewed as one or more subtrees of the tree structure.

Let’s take a look at a simple example. For example, a company’s organizational structure can be displayed as a tree structure. The top level is the general manager (root node), and there are multiple department managers (child nodes) below. Each There are multiple employees (leaf nodes) under the department manager.

2. The principle of converting a two-dimensional array into a tree structure

Converting a two-dimensional array into a tree structure can be regarded as a set of flat data, using its internal relationships to convert The process of organizing it into a tree data structure. The conversion process can be implemented recursively. The specific steps are as follows:

1. Find the root node data from the two-dimensional array, remove it from the array, and then recursively search for the child nodes under the root node.
2. Traverse the entire array, push the child nodes in each element onto the stack, and then recursively search for the child nodes under the child node.
3. The recursive end condition is that the current array is empty or there are no child nodes of the current node.

According to the above three steps, the function of converting a two-dimensional array to a tree can be realized.

3. Code Implementation

Let’s use a practical example to demonstrate how to convert a two-dimensional array into a tree structure. Suppose we have the following two-dimensional array:

$data = array(
    array('id'=>1,'name'=>'节点1','pid'=>0),
    array('id'=>2,'name'=>'节点2','pid'=>1),
    array('id'=>3,'name'=>'节点3','pid'=>2),
    array('id'=>4,'name'=>'节点4','pid'=>2),
    array('id'=>5,'name'=>'节点5','pid'=>0)
);

The array contains 5 nodes, where id represents the unique identifier of the node, name represents the node name, and pid represents the node's parent node id.

Now we need to convert this two-dimensional array into the following tree structure:

Array
(
    [0] => Array
        (
            [id] => 1
            [name] => 节点1
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 2
                            [name] => 节点2
                            [children] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 3
                                            [name] => 节点3
                                            [children] => Array()
                                        )

                                    [1] => Array
                                        (
                                            [id] => 4
                                            [name] => 节点4
                                            [children] => Array()
                                        )

                                )

                        )

                )

        )

    [1] => Array
        (
            [id] => 5
            [name] => 节点5
            [children] => Array()
        )

)

The specific implementation process is as follows:

function buildTree(&$data,$pid = 0){
    $tree = array();
    foreach($data as $k=>$v){
        if($v['pid'] == $pid){
            $temp = $v;
            $temp['children'] = buildTree($data,$v['id']);
            $tree[] = $temp;
            unset($data[$k]);
        }
    }
    return $tree;
}

$data =    array(
    array('id'=>1,'name'=>'节点1','pid'=>0),
    array('id'=>2,'name'=>'节点2','pid'=>1),
    array('id'=>3,'name'=>'节点3','pid'=>2),
    array('id'=>4,'name'=>'节点4','pid'=>2),
    array('id'=>5,'name'=>'节点5','pid'=>0)
);
print_r(buildTree($data));

In the above code, the buildTree function is first instantiated An empty array $tree, then traverse the entire $data array, store all data with pid $pid into the $tree array, and recursively search for all child nodes under $pid, and then return the $tree array. If the $data array is empty or there are no child nodes of the current node, the recursion ends.

4. Summary

Through the above code, we can see that the process of converting a two-dimensional array into a tree structure is very simple. We only need to use recursion to convert all nodes in sequence. Just organize it into a tree structure. This is very useful for data processing and display in web development, and can realize different functions of data display and data structure organization in different scenarios.

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