Online PHP editor | refs for Z6bUe

<?php $array = array( 98 => array( 'City' => 'Caracas', 'Country' => 'Venezuela', 'Continent' => 'Latin America', ), 99 => array( 'City' => 'Cairo', 'Country' => 'Egypt', 'Continent' => 'Middle East', ), 105 => array( 'City' => 'Abu Dhabi', 'Country' => 'United Arab Emirates', 'Continent' => 'Middle East', ), 106 => array( 'City' => 'Dubai', 'Country' => 'United Arab Emirates', 'Continent' => 'Middle East', ), 107 => array( 'City' => 'Montreal', 'Country' => 'Canada', 'Continent' => 'North America', ) ); $result = []; foreach ( $array as [ 'Continent' => $a, 'Country' => $b, 'City' => $result[$a][$b][] ] ); var_export($result);