- array_intersect_key: documentation ( source)
- array_combine: documentation ( source)
- print_r: documentation ( source)
- array_flip: documentation ( source)
- range: documentation ( source)
<?php
$a = [ 'firstname' , 'bob' , 'lastname' , 'alex' ];
$new = array_combine(
array_intersect_key($a, array_flip(range(0, count($a) - 1, 2))),
array_intersect_key($a, array_flip(range(1, count($a) - 1, 2)))
);
print_r($new);