Reorder a PHP array, moving items up or down

gistfile1.php

<?php
/*
 A quick set of functions to move items in a non-associative array
 up or down by one, shifting the items around it appropriately.
 
 Original usage was to for a set of UP and DOWN buttons to 
 manipulate the order of an array of items stored in Wordpress option.
*/

$a = array('a','b','c','d','e');

function down($a,$x) {
	if( count($a)-1 > $x ) {
		$b = array_slice($a,0,$x,true);
		$b[] = $a[$x+1];
		$b[] = $a[$x];
		$b += array_slice($a,$x+2,count($a),true);
		return($b);
	} else { return $a; }
}

function up($a,$x) {
	if( $x > 0 and $x < count($a) ) {
		$b = array_slice($a,0,($x-1),true);
		$b[] = $a[$x];
		$b[] = $a[$x-1];
		$b += array_slice($a,($x+1),count($a),true);
		return($b);
	} else { return $a; }
}

// Start
print_r($a);
/* Output
Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
)
*/

// Move item 4 up
print_r(up($a,4));
/* Output
Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => e
    [4] => d
)
*/

// Move item 0 down
print_r(down($a,0));
/* Output
Array
(
    [0] => b
    [1] => a
    [2] => c
    [3] => d
    [4] => e
)
*/

// Test, move the bottom item down (ie. do nothing)
print_r(down($a,4));
/* Output
Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
)
*/

// Test, move the top item up (ie. do nothing)
print_r(up($a,0));
/* Output
Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
)
*/