Question

I’m using a single mysql query to create a multidimensional array for nested results (categories and subcategories).

Query

SELECT `categories`.`cat_title`, `subcategories`.`sub_cat_id`, `subcategories`.`sub_cat_title` 
FROM (`categories`) 
LEFT JOIN `subcategories` 
ON `subcategories`.`cat_id` = `categories`.`cat_id` 
ORDER BY `categories`.`cat_title

Creating multidimensional array

$array = array(); 

foreach ($query->result_array() as $row): //query result as a pure array
        $array[$row['cat_title']][] = $row['sub_cat_title'];
endforeach; 

return $array;

The above returns categories and and their respective subcategories.

 Array ( 
   [Art] => Array ( [0] => Graphic Design [1] => Painting )
   [Literature] => Array ( [0] => Science Fiction [1] => Poetry [2] => Fiction ) 
   [Science] => Array ( [0] => Environmental ) 
 )

Is it possible to replace the array keys with query data like the subcategory id sub_cat_id? For example

[Literature] => Array ( [8] => Science Fiction [94] => Poetry [5] => Fiction )  

Answer 1

Yes, set it in the loop:

$array[ $row['cat_title'] ][ $row['sub_cat_id'] ] = $row['sub_cat_title'];

But, $array[$row['cat_title']] might not be set yet, so you should add this check beforehand:

if( !isset( $array[$row['cat_title']])) {
    $array[$row['cat_title']] = array();
}

Your original code doesn’t need this check since $array[] will not generate any notices/warnings, but when you try to set a specific key, that will generate a notice/warning if the variable isn’t already declared as an array.