function array_flatten($array, &$new_array = array(), $index = '') 
{
    foreach ($array as $key => $value) 
    {
    	if (!empty($index)) 
    	{
            $key = $index.'_'.$key;
        }
 
        if (is_array($value)) 
        {
            $new_array = array_flatten($value, $new_array, $key);
        } 
        else 
        {
            $new_array[$key] = $value;
        }        
    }
 
    return $new_array;
}