Sorting One Array at a Time

PHP functions for sorting an array

Effect	Ascending	Descending	User-defined order
Sort array by values, then reassign indices starting with 0	sort( )	rsort( )	usort( )
Sort array by values	asort( )	arsort( )	uasort( )
Sort array by keys	ksort( )	krsort( )	uksort( )

The sort( ), rsort( ), and usort( ) functions are designed to work on indexed arrays because they assign new numeric keys to represent the ordering. They're useful when you need to answer questions such as, "What are the top 10 scores?" and "Who's the third person in alphabetical order?" The other sort functions can be used on indexed arrays, but you'll only be able to access the sorted ordering by using traversal functions such as foreach and next 

To sort names into ascending alphabetical order, you'd use this:

    $names = array('cath', 'angela', 'brad', 'dave');
    sort($names);                // $names is now 'angela', 'brad', 'cath', 'dave'

To get them in reverse alphabetic order, simply call rsort( ) instead of sort( ).

If you have an associative array mapping usernames to minutes of login time, you can use arsort( ) to display a table of the top three, as shown here:

    $logins = array('njt' => 415,
                    'kt'  => 492,
                    'rl'  => 652,
                    'jht' => 441,
                    'jj'  => 441,
                    'wt'  => 402);
    arsort($logins);
    $num_printed = 0;
    echo("<table>\n");
    foreach ($logins as $user => $time ) {
      echo("<tr><td>$user</td><td>$time</td></tr>\n");
      if (++$num_printed == 3) {
        break;                   // stop after three
      }
    }
    echo("</table>\n");
    <table>
    <tr><td>rl</td><td>652</td></tr>
    <tr><td>kt</td><td>492</td></tr>
    <tr><td>jht</td><td>441</td></tr>
    </table>

If you want that table displayed in ascending order by username, use ksort( ):

    ksort($logins);
    echo("<table>\n");
    foreach ($logins as $user => $time) {
      echo("<tr><td>$user</td><td>$time</td></tr>\n");
    }
    echo("</table>\n");
    <table>
    <tr><td>jht</td><td>441</td></tr>
    <tr><td>jj</td><td>441</td></tr>
    <tr><td>kt</td><td>492</td></tr>
    <tr><td>njt</td><td>415</td></tr>
    <tr><td>rl</td><td>652</td></tr>
    <tr><td>wt</td><td>402</td></tr>
    </table>

User-defined ordering requires that you provide a function that takes two values and returns a value that specifies the order of the two values in the sorted array. The function should return 1 if the first value is greater than the second, -1 if the first value is less than the second, and 0 if the values are the same for the purposes of your custom sort order.

 a program that lets you try the various sorting functions on the same data.