convert normal array in nested array with php - php

Question

I have a hierarchical database table like below
ID Name Subcategory ParentID
1 ABC 0
2 DEF QFE 0
3 QFE XYZ 2
4 XYZ MNJ 3
From Thant I have got PHP array like below
$array_name = array(
array('ID' => '1', 'Name' => 'ABC', 'Subcategory' => '', 'ParentID' => '0'),
array('ID' => '2', 'Name' => 'DEF', 'Subcategory' => 'QFE', 'ParentID' => '0'),
array('ID' => '3', 'Name' => 'QFE', 'Subcategory' => 'XYZ', 'ParentID' => '2'),
array('ID' => '4', 'Name' => 'XYZ', 'Subcategory' => 'MNJ', 'ParentID' => '3')
);
but I want array like below
$array_name = array(
array('ID' => '1', 'Name' => 'ABC', 'Subcategory' => '', 'ParentID' => '0'),
array('ID' => '2', 'Name' => 'DEF', 'Subcategory' => array('ID' => '3', 'Name' => 'QFE', 'Subcategory' => array('ID' => '4', 'Name' => 'XYZ', 'Subcategory' => 'MNJ', 'ParentID' => '3'), 'ParentID' => '2'), 'ParentID' => '0'),
);
I want a function which checks is that row have some Subcategory or not and if a row has Subcategory then get that subcategory row as an array and make one array with all category and Subcategory
for that, I have tried to make a function which is given below
function find_subcategory($ID,$con){
$table_name ="SELECT * FROM `table_name` WHERE `parent_id` = '$ID'";
$table_name_result = mysqli_query($con,$table_name);
$category_array = array();
if(mysqli_num_rows($table_name_result)) {
while($row = mysqli_fetch_assoc($table_name_result)) {
$Subcategory= $row['Subcategory'];
$ID = $row['ID'];
if ($Subcategory== '') {
$find_subcategory = find_subcategory($ID,$con);
$row['Subcategory'] = $find_subcategory;
$category_array[] = $row;
}else{
$category_array[] = $row;
}
}
}
return json_encode(array('tbl_category'=>$category_array));
}
but this function is not working to get all the subcategories of one category.
can anybody help me with this

Answer 1

Rather than create a recursive routine, which executes the SQL for each level, this instead reads all of the categories in and them assembles them into the hierarchy.
Note that it reads them in reverse order so that when it assembles them, each subcategory is always read before the parent (More details in code comments)...
$table_name ="SELECT * FROM `category` ORDER BY parent_id DESC, id desc";
$table_name_result = mysqli_query($con,$table_name);
$categories = mysqli_fetch_all($table_name_result, MYSQLI_ASSOC);
$output= [];
foreach ( $categories as $category) {
// If there is a parent for this item
if ( !empty ($category['parent_id']) ) {
// Set basic details
$output[$category['parent_id']]['Subcategory'][$category['id']] = $category;
// If there is already some data (subcategories)
if ( isset($output[$category['id']]) ){
// Copy subcategories
$output[$category['parent_id']]['Subcategory'][$category['id']] +=
$output[$category['id']];
// Remove old node
unset ( $output[$category['id']] );
}
}
else {
// Add in category data (allow for existing data to be added
$output[$category['id']] = $category + ($output[$category['id']]??[]);
}
}

Answer 2

I successfully implemented and tested a recursive routine to solve this. However, for performance reasons I had to decouple the access to the database from the recursive call.
First, you fetch your query into an array as you already have and then recursively rearrange the elements so that the keys are nested in the proper order.
Pretty much of the explanations I'd like to put here are put as comments in the code.
$array_name = array(
array('ID' => '1', 'Name' => 'ABC', 'Subcategory' => '', 'ParentID' => '0'),
array('ID' => '2', 'Name' => 'DEF', 'Subcategory' => 'QFE', 'ParentID' => '0'),
array('ID' => '3', 'Name' => 'QFE', 'Subcategory' => 'XYZ', 'ParentID' => '2'),
array('ID' => '4', 'Name' => 'XYZ', 'Subcategory' => 'MNJ', 'ParentID' => '3'),
array('ID' => '5', 'Name' => 'XYY', 'Subcategory' => 'MNJ', 'ParentID' => '1')
);
// recreate nested array
function get_nested_array($arr) {
$new_arr = array(); // new array to collect each top level element with nesting
foreach ($arr as $key => $value) {
// only top level elements would appear here as they would not be nested
if($value['ParentID'] == '0') {
array_push($new_arr, get_nested_item($value, $arr));
}
}
return $new_arr;
}
// recursive function to perform nesting on each element
function get_nested_item($hay, $stack) {
foreach ($stack as $key => $value) {
if ($hay['ID'] == $value['ParentID']) {
$index = get_key($hay, $stack);
// reduce $stack size by removing the HAY from the STACK
// recursion terminates when $stack size is 0
$stack = $index >= 0 ? array_splice($stack, $index) : [];
// update subcategory of the found nesting
$hay['Subcategory'] = get_nested_item($value, $stack);
}
}
return $hay;
}
// get the position of $hay in a $stack using the ID
function get_key($hay, $stack) {
foreach ($stack as $key => $value) {
if($hay['ID'] == $value['ID']) return $key;
}
return -1;
}
// print array so that it understandable
function print_array($arr) {
foreach ($arr as $key => $value) {
print_r($value);
echo "<br>";
}
}
// Test case
// print array before nesting
print_array($array_name);
echo"<br>";
// print array after nesting
$new_array = get_nested_array($array_name);
print_array($new_array);