Online PHP editor | output for b6UiZ

<?php $a1 = [ 'from' => 'Paris', 'to' => 'Marseille', ]; $a2 = [ 'from' => 'Marseille', 'to' => 'Valencia', ]; $a3 = [ 'from' => 'Valencia', 'to' => 'Algiers', ]; $a4 = [ 'from' => 'Algiers', 'to' => 'Abu Dhabi', ]; $route = array($a4, $a3, $a1, $a2); $from = array_column($route, 'from'); $to = array_column($route, 'to'); $start = array_diff($from, $to); $sortedRoute = [$route[key($start)]]; $start = $route[key($start)]['to']; while (true) { $key = array_search($start, $from); if ($key === false) break; $sortedRoute[] = $route[$key]; $start = $route[$key]['to']; } var_dump($sortedRoute);