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<?php $categories = array( 'category_1' => array( 'name' => 'Category 1', 'column' => '1' ), 'category_2' => array( 'name' => 'Category 2', 'column' => '2' ), 'category_3' => array( 'name' => 'Category 2', 'column' => '1' ), 'category_4' => array( 'name' => 'Category 4', 'column' => '3' ), 'category_4' => array( 'name' => 'Category 4', 'column' => '2' ), ); $output = array(); foreach($categories as $catName => $category) { $columnNum = $category['column']; if (!isset($output[$columnNum] )) { $output[$columnNum] = array($catName); } else { $output[$columnNum][] = $catName; } } var_dump($output);
Output for 4.3.0 - 5.6.28, hhvm-3.10.0 - 3.12.0, 7.0.0 - 7.1.0
array(2) { [1]=> array(2) { [0]=> string(10) "category_1" [1]=> string(10) "category_3" } [2]=> array(2) { [0]=> string(10) "category_2" [1]=> string(10) "category_4" } }