Online PHP editor | output for GtY49

<?php $array = [ 'relation' => 'AND', [ 'taxonomy' => 'merk', 'field' => 'slug', 'terms' => ['coral'] ], [ 'taxonomy' => 'foo', 'field' => 'bar', 'terms' => ['stackoverflow'] ], [ 'taxonomy' => 'merk', 'field' => 'slug', 'terms' => ['deluxe', 'ultra'] ] ]; foreach ($array as $key => &$item) { if (is_array($item) && isset($item['taxonomy'], $item['field'])) { $id = $item['taxonomy'] . '_' . $item['field']; if (!isset($ref[$id])) { $ref[$id] = &$item['terms']; } else { array_push($ref[$id], ...$item['terms']); unset($array[$key]); } } } var_export($array);