array_multisort

Running PHP 4.0.0 I had to do this to get the function to work:
array_multisort(&$array1, SORT_DESC, &$array2, &$array3);
in order to get this to return the sorted array(s).

if you're having problems with array_multisort changing variables in global
space when it is called inside a function and you're not passing in the
function parameters by reference you can alleviate the problem by calling
array_multisort with its parameters by reference, eg,
array_multisort(&$a, SORT_DESC, &$b);  More details here in my bug
report:
http://www.php.net/bugs.php?id=12936

If you have an array that contains output from a SQL SELECT statment and
you want to sort the array on a column, you have to create a separate array
containing the values of that column like so:

//Get table output into $rows array
$result = mysql_query("SELECT field1, field2 from table");
while ($rows[] = mysql_fetch_array($result)) {}

//Sort on field2
foreach ($rows as $val) {
        $sortarray[] = $val['field2'];
}
array_multisort($rows, $sortarray);

//Now, $rows is sorted on field2

If anyone knows an easier way to do this, please let us know!

If you want to sort a multidimentionnal array based on a certain row, the
easiest way I found was using usort() and a comparison function of my own.

The comparison function is called with two elements of the array. Then, in
the function, as the two elements are also arrays (we are dealing with a
multidimentionnal one), the comparison can be made on any row:
if ($a[2] > $b[2]) return 1; ...

See the definition of usort() for that.

EXAMPLE: You have two arrays where one has results from a test and the
other names of the participants and you need to graph these results in
descending order, but keeping the name and score relationship in tact.

<?
$scores=array(90, 10, 70, 100);
$participants=array("liam","val","john","richard");
array_multisort($scores,SORT_DESC,$participants);

#  would now produce:
#  $scores[0]=100; $participants[0]="richard"; 
#  $scores[1]=90;  $participants[1]="liam";   
#  etc..
?>

This example for sorting SQL results is very usefull, except the author
mixed up the array_multisort() arguments :

//Get table output into $rows array
$result = mysql_query("SELECT field1, field2 from table");
while ($rows[] = mysql_fetch_array($result)) {}

//Sort on field2
foreach ($rows as $val) {
        $sortarray[] = $val['field2'];
}
array_multisort($sortarray,$rows);

//Now, $rows is sorted on field2

it seems that you always have to provide the arrays to the funktion by
using &$arrayname. anything else didn't work for me....

regards
Mike

The original post is correct... not the second post on this code:

The code from If you have an array that contains output from a SQL SELECT
statment and
you want to sort the array on a column, you have to create a separate
array containing the values of that column like so:

//Get table output into $rows array
$result = mysql_query("SELECT field1, field2 from table");
while ($rows[] = mysql_fetch_array($result)) {}

//Sort on field2
foreach ($rows as $val) {
        $sortarray[] = $val['field2'];
}
array_multisort($rows, $sortarray);

//Now, $rows is sorted on field2

If anyone knows an easier way to do this, please let us know!

It can be very useful to use array_keys(*) as one of the arguments. 
Example: you have an associative array of items and quantities, where the
item is used as a key. Say you want to sort the array by descending
quantity, and sort items with the same quantity in alphabetical order. Here
is the code:

$arr["potato"] = 5; 
$arr["orange"] = 3; 
$arr["apple"] = 3; 
$arr["lemon"] = 4; 
$arr["onion"] = 5; 
$arr["grapefruit"] = 3;
array_multisort ($arr, SORT_DESC, array_keys ($arr));
print_r ($arr);

Here is the output:

Array 
( 
    [onion] => 5 
    [potato] => 5 
    [lemon] => 4 
    [apple] => 3 
    [grapefruit] => 3 
    [orange] => 3 
)

the 13-Apr note by richard is really handy when you don't have database
acces/support and you're using multiple arrays instead. It can be used for
example to sort topics in a forum on 'last edited'. Make sure you have 2
arrays, one with the different topics (for example filenames) and one with
the 'last-edited times'

array_multisort($topicfilenames,SORT_DESC,$lasteditedtimes);