Array Manipulation With PHP4 - Sorting Things Out
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If you need to, you can rearrange the elements within an array with PHP's numerous sorting functions. The simplest of these is the array_reverse() function, which merely reverses the order of elements within an array.

<?
// create array
$trio = array("huey", "dewey", "louie");

// returns ("louie", "dewey", "huey")
array_reverse($trio);
?>

The shuffle() function randomly reshuffles the elements within an array,

<?
// create array
$trio = array("huey", "dewey", "louie");

// shuffles elements of array to return ("dewey", "louie", "huey")
shuffle($trio);
?>

while the array_unique() function helps you strip out duplicate values from an array.

<?
// create array
$clones = array("Tom", "Tom", "Harry", "Tom", "Harry", "Harry", "Harry",
"Tom");

// returns ("Tom", "Harry")
array_unique($clones);
?>

The sort() function can be used to sort an array alphabetically or numerically,

<?
// create array
$animals = array("antelope", "zebra", "skunk", "baboon", "viper");

// returns ("antelope", "baboon", "skunk", "viper", "zebra")
sort($animals);
?>

while the rsort() function does the same thing (just the other way around).

<?
// create array
$animals = array("antelope", "zebra", "skunk", "baboon", "viper");

// returns ("zebra", "viper", "skunk", "baboon", "antelope")
rsort($animals);
?>

The ksort() function sorts a hash by key (you can reverse the sort order with the krsort() function),

<?
// create array
$numbers = array("2" => "duet", "13" => "baker's dozen", "-15" =>
"temperature", "3" => "stooges");

// returns ("-15" => "temperature", "2" => "duet", "3" => "stooges", "13"
=> "baker's dozen")
ksort($numbers);

// returns ("13" => "baker's dozen", "3" => "stooges", "2" => "duet", "-15"
=> "temperature")
krsort($numbers);
?>

The usort() function lets you apply your own sort function to the elements of an array. The function that you define must be capable of comparing two values, and must return a positive, negative or zero value depending on whether the first value being compared is greater than, less than or equal to the second value.

An example might help to make this clearer. The following code snippet defines a custom sort function, which arranges elements according to their length.

<?
// compare two values on length
function check_length($str1, $str2)
{
	if (strlen($str1) > strlen($str2))
	{
	return 1;
	}
	elseif (strlen($str1) == strlen($str2))
	{
	return 0;
	}
	else
	{
	return -1;
	}
}

// create array
$animals = array("antelope", "zebra", "skunk", "baboon", "viper", "yak");

// returns ("yak", "skunk", "viper", "zebra", "baboon", "antelope")
usort($animals, "check_length");
?>

In a similar manner, you can apply a user-defined comparison function to the keys of a hash with the uksort() function - I'll leave this to you to experiment with.

The natsort() function makes it possible to sort array elements the way a human - rather than a computer - would. Consider the following example:

<?
// create array
$mixed = array(1, "zebra", "skunk", "baboon", 13, "viper", -99, "yak");

// returns ("-99", "baboon", "skunk", "viper", "yak", "zebra", "1", "13")
sort($mixed);

// returns ("-99", "1", "13", "baboon", "skunk", "viper", "yak", "zebra")
natsort($mixed);
?>

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