PHP get array keys from array

$numbers  = array(
	'one' => 'one'
	,'two' => 'two'
	,'three' => 'three'
	,'four' => 'four'
	,'five' => 'five'
	,'six' => 'six'
	,'seven' => 'seven'
	,'eight' => 'eight'
	,'nine' => 'nine'
	,'ten' => 'ten'
);

foreach($numbers as $num_key=>$num_val){
	$array_keys[$num_key] =$num_key;
}
//RESULT

Array
(
    [one] => one
    [two] => two
    [three] => three
    [four] => four
    [five] => five
    [six] => six
    [seven] => seven
    [eight] => eight
    [nine] => nine
    [ten] => ten
)

array(0,1,2,3,3,4,5,5,7,8,7,7)
foreach($numbers as $num_key=>$num_val){
 $array_keys[$num_key] =$num_key;
}

//RESULT

Array
(
    [0] => 0
    [1] => 1
    [2] => 2
    [3] => 3
    [4] => 4
    [5] => 5
    [6] => 6
    [7] => 7
    [8] => 8
    [9] => 9
    [10] => 10
    [11] => 11
)