Online PHP editor | refs for tVYJJ

<?php $array = [ ['toxic', 'irritant', 'flammable'], ['toxic', 'irritant'], ['toxic'], ]; $iterator = new RecursiveIteratorIterator( new RecursiveArrayIterator($array) ); $result = []; foreach ($iterator as $leafNode) { $result[$leafNode] = ($result[$leafNode] ?? 0) + 1; } var_export($result);