How to increase by 1 all keys in an array?

Question

What is the simplest solution to increase by 1 all keys in an array?

BEFORE:

$arr[0] = \'a\';
$arr[1] = \'b\';
$arr[2] = \'c\';
         


        

Answer 1

Well, there's one very simple way to do it:

$arr = array('a', 'b', 'c');
array_unshift($arr, null);
unset($arr[0]);
print_r($arr);
/* 
Array
(
    [1] => a
    [2] => b
    [3] => c
)
*/

Will work only for simple dense arrays, of course.

And this is most untrivial (yet both a one-liner AND working for both dense and sparse arrays) way:

$arr = array_flip(array_map(function($el){ return $el + 1; }, array_flip($arr)));