PHP: 'rotate' an array?

Question

is it possible to easily \'rotate\' an array in PHP ?

Like this: 1, 2, 3, 4 -> 2, 3 ,4 ,1

Is there some kind of built-in PHP function for this?

Answer 1

you can use this function:

    function arr_rotate(&$array,$rotate_count) {
        for ($i = 0; $i < $rotate_count; $i++) {
            array_push($array, array_shift($array));
        }
    }

usage:

    $xarr = array('1','2','3','4','5');
    arr_rotate($xarr, 2);
    print_r($xarr);

result:

 Array ( [0] => 3 [1] => 4 [2] => 5 [3] => 1 [4] => 2 )

Answer 2

Use array_shift and array_push.

Answer 3

Most of the current answers are correct, but only if you don't care about your indices:

$arr = array('foo' => 'bar', 'baz' => 'qux', 'wibble' => 'wobble');
array_push($arr, array_shift($arr));
print_r($arr);

Output:

Array
(
    [baz] => qux
    [wibble] => wobble
    [0] => bar
)

To preserve your indices you can do something like:

$arr = array('foo' => 'bar', 'baz' => 'qux', 'wibble' => 'wobble');

$keys = array_keys($arr);
$val = $arr[$keys[0]];
unset($arr[$keys[0]]);
$arr[$keys[0]] = $val;

print_r($arr);

Output:

Array
(
    [baz] => qux
    [wibble] => wobble
    [foo] => bar
)

Perhaps someone can do the rotation more succinctly than my four-line method, but this works anyway.

Answer 4

There's a task about array rotation on Hackerrank: https://www.hackerrank.com/challenges/array-left-rotation/problem.

And proposed solution with array_push and array_shift will work for all test cases except the last one, which fails due to timeout. So, array_push and array_shift will give you not the fastest solution.

Here's the faster approach:

function leftRotation(array $array, $n) {
   for ($i = 0; $i < $n; $i++) {
       $value = array[$i]; unset(array[$i]); array[] = $value;
   }
   return array;
}

Answer 5

The logic is to swap the elements. Algorithm may look like -

 for i = 0 to arrayLength - 1
    swap( array[i], array[i+1] )     // Now array[i] has array[i+1] value and 
                                     // array[i+1] has array[i] value.

Answer 6

No. Check the documentation for array_shift and its related functions for some tools you can use to write one. There might even be an array_rotate function implemented in the comments of that page.

It's also worth reading through the array functions listed on the left-hand sidebar to get a full understanding of what array functions are available in PHP.