The keys are maintained with the removed key missing but they can be rearranged by doing this:
$array = array(1,2,3,4,5);
unset($array[2]);
$arranged = array_values($array);
print_r($arranged);
Outputs:
Array
(
[0] => 1
[1] => 2
[2] => 4
[3] => 5
)
Notice that if we do the following without rearranging:
unset($array[2]);
$array[]=3;
The index of the value 3 will be 5 because it will be pushed to the end of the array and will not try to check or replace missing index. This is important to remember when using FOR LOOP with index access.