How to flatten a PHP array

function true_flatten(array $array, array $parents = []) { $return = []; foreach ($array as $k => $value) { $p = empty($parents) ? [$k] : [...$parents, $k]; if (is_array($value)) { $return = [...$return, ...true_flatten($value, $p)]; } else { $return[implode('_', $p)] = $value; } } return $return; } 

$r = [ 'a' => 'value1', 'b' => [ 'c' => 'value1.1', 'd' => 'value1.2', ], 'e' => 'value2', 'f' => [ 'j' => [ 'k' => 'value2.1', 'm' => 'value2.2', 'n' => 'value2.3', ], ], 'o' => 'value3', 'p' => [ 'some' => [ 'very' => [ 'deep' => [ 'item' => [ 'first', 'second', ] ] ] ] ], 'q' => 'value5', ]; // sample data 

{ "a": "value1", "b_c": "value1.1", "b_d": "value1.2", "e": "value2", "f_j_k": "value2.1", "f_j_m": "value2.2", "f_j_n": "value2.3", "o": "value3", "p_some_very_deep_item_0": "first", "p_some_very_deep_item_1": "second", "q": "value5" }