Flatten a multidimensional array with keys separated by _

falatten_array.php

/**
 * Flatten a multi dimension array. For an associative array the child keys are separated by underscore(_).
 * @author Muntasir Mohiuddin
 * @param array $a multidimensional array to flatten
 * @param array $a multidimensional array to save values
 * @param string $p previous parents separated by underscore(_)
 * @return array all flattened keys
 */
function flatten_array($a, &$r, $p=NULL){
	foreach($a as $k => $v) { 
	    $keys[] = $k; 

    	if(is_null($p)){
    		$_p = $k;
    	} else {
    		$_p = $p . "_" . $k;
    	}
    	
	    if (is_array($a[$k])) {
	        $keys = array_merge($keys, flatten_array($a[$k], $r, $_p)); 
	    } else {
	    	$r[$_p] = $v;
	    }
	} 
	
	return $keys; 
}

$property_value = array(    	
	'a' => 'VALUE A',
	'b' => 'VALUE B',
	'c' => array(
		'd' => 'VALUE d',
		'e' => 'VALUE E',
		'f' => array(
			'g' => 'VALUE G'
		),
	),
	'h' => 'VALUE H',
	'i' => array(
		'j' => 'VALUE J',
		'k' => array(
			'l' => 'VALUE L',
			'm' => array(
				'n' => 'VALUE n',
			),
		),
	),
);


$flatten_values = array();
flatten_array($property_value, $flatten_values);

/* OUTPUT
Array
(
    [a] => VALUE A
    [b] => VALUE B
    [c_d] => VALUE d
    [c_e] => VALUE E
    [c_f_g] => VALUE G
    [h] => VALUE H
    [i_j] => VALUE J
    [i_k_l] => VALUE L
    [i_k_m_n] => VALUE n
)
*/