Reindex array by increasing and decreasing all of top indexes

Question

First, I have to list what I have found

How to Remove Array Element and Then Re-Index Array?

PHP reindex array?

They did not make sense in my case. I have fallen into ridiculous request and I've force to find the way out, then please don't ask me why I want to do that.

I have below array

$input = array(
          0=>array('a', 'b'=>array('c')),
          1=>array('b', 'c'=>array('d')),
          2=>array('c', 'd'=>array('e')),
        );

I want to increase all of keys by 1 or decrease by 1 (acceptable to index is negative int number)

Here is expected result

//after increased by 1
$input = array(
          1=>array('a', 'b'=>array('c')),
          2=>array('b', 'c'=>array('d')),
          3=>array('c', 'd'=>array('e')),
        );

or

//after decreased by 1
$input = array(
          -1=>array('a', 'b'=>array('c')),
          0=>array('b', 'c'=>array('d')),
          1=>array('c', 'd'=>array('e')),
        );

The closet answer I got here from raina77ow in the question How to increase by 1 all keys in an array?

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

But it just works with simple array key pairs, if array value is other array instead of a string or integer, it would raise the exception

array_flip(): Can only flip STRING and INTEGER values!

The thing what I could think is handling the array to swap roster manually, it would be the final way if there were not any other workaround.

Any help is appreciated!

Answer 1

The easiest way would probably to use foreach and make a new array... like this:

$new = array();
foreach($arr as $k=>$v) {
    $new[$k+1] = $v; // either increase
    $new[$k-1] = $v; // or decrease
}

You can also perform the operation by passing the original array by reference.

Answer 2

This should so the trick.

    // Increase by one
    $input = array_combine(
        array_map(function($value) {
            return $value += 1;
        }, array_keys($input)), $input
    );