Specifications

The function asort() orders the array according to the value of each element. In the array, the

values are the prices and the keys are the textual descriptions. If instead of sorting by price we

want to sort by description, we use ksort(), which sorts by key rather than value. This code

will result in the keys of the array being ordered alphabetically—Oil, Spark Plugs, Tires.

$prices = array( “Tires”=>100, “Oil”=>10, “Spark Plugs”=>4 );

ksort($prices);

Sorting in Reverse

You have seen sort(), asort(), and ksort(). These three different sorting functions all sort

an array into ascending order. Each of these functions has a matching reverse sort function to

sort an array into descending order. The reverse versions are called rsort(), arsort(), and

krsort().

The reverse sort functions are used in the same way as the sorting functions. The rsort()

function sorts a single dimensional numerically indexed array into descending order. The

arsort() function sorts a one-dimensional associative array into descending order using the

value of each element. The krsort() function sorts a one-dimensional associative array into

descending order using the key of each element.

Sorting Multidimensional Arrays

Sorting arrays with more than one dimension, or by something other than alphabetical or

numerical order, is more complicated. PHP knows how to compare two numbers or two text

strings, but in a multidimensional array, each element is an array. PHP does not know how to

compare two arrays, so you need to create a method to compare them. Most of the time, the

order of the words or numbers is fairly obvious—but for complicated objects, it becomes more

problematic.

User Defined Sorts

Here is the definition of a two-dimensional array we used earlier. This array stores Bob’s three

products with a code, a description, and a price for each.

$products = array( array( “TIR”, “Tires”, 100 ),

array( “OIL”, “Oil”, 10 ),

array( “SPK”, “Spark Plugs”, 4 ) );

If we sort this array, what order will the values end up in? Because we know what the contents

represent, there are at least two useful orders. We might want the products sorted into alphabet-

ical order using the description or by numeric order by the price. Either result is possible, but

we need to use the function usort() and tell PHP how to compare the items. To do this, we

need to write our own comparison function.

Using PHP

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