sort

Simple function to sort an array by a specific key. Maintains index association.

<?php

function array_sort($array, $on, $order=SORT_ASC)
{
    $new_array = array();
    $sortable_array = array();

    if (count($array) > 0) {
        foreach ($array as $k => $v) {
            if (is_array($v)) {
                foreach ($v as $k2 => $v2) {
                    if ($k2 == $on) {
                        $sortable_array[$k] = $v2;
                    }
                }
            } else {
                $sortable_array[$k] = $v;
            }
        }

        switch ($order) {
            case SORT_ASC:
                asort($sortable_array);
            break;
            case SORT_DESC:
                arsort($sortable_array);
            break;
        }

        foreach ($sortable_array as $k => $v) {
            $new_array[$k] = $array[$k];
        }
    }

    return $new_array;
}

$people = array(
    12345 => array(
        'id' => 12345,
        'first_name' => 'Joe',
        'surname' => 'Bloggs',
        'age' => 23,
        'sex' => 'm'
    ),
    12346 => array(
        'id' => 12346,
        'first_name' => 'Adam',
        'surname' => 'Smith',
        'age' => 18,
        'sex' => 'm'
    ),
    12347 => array(
        'id' => 12347,
        'first_name' => 'Amy',
        'surname' => 'Jones',
        'age' => 21,
        'sex' => 'f'
    )
);

print_r(array_sort($people, 'age', SORT_DESC)); // Sort by oldest first
print_r(array_sort($people, 'surname', SORT_ASC)); // Sort by surname

/*
Array
(
    [12345] => Array
        (
            [id] => 12345
            [first_name] => Joe
            [surname] => Bloggs
            [age] => 23
            [sex] => m
        )
 
    [12347] => Array
        (
            [id] => 12347
            [first_name] => Amy
            [surname] => Jones
            [age] => 21
            [sex] => f
        )
 
    [12346] => Array
        (
            [id] => 12346
            [first_name] => Adam
            [surname] => Smith
            [age] => 18
            [sex] => m
        )
 
)
Array
(
    [12345] => Array
        (
            [id] => 12345
            [first_name] => Joe
            [surname] => Bloggs
            [age] => 23
            [sex] => m
        )
 
    [12347] => Array
        (
            [id] => 12347
            [first_name] => Amy
            [surname] => Jones
            [age] => 21
            [sex] => f
        )
 
    [12346] => Array
        (
            [id] => 12346
            [first_name] => Adam
            [surname] => Smith
            [age] => 18
            [sex] => m
        )
 
)
*/

?>

unless you specify the second argument, "regular" comparisons will be used. I quote from the page on comparison operators:
"If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically."
What this means is that "10" < "1a", and "1a" < "2", but "10" > "2". In other words, regular PHP string comparisons are not transitive.
This implies that the output of sort() can in rare cases depend on the order of the input array:
<?php
function echo_sorted($a)
{
   echo "{$a[0]} {$a[1]} {$a[2]}";
   sort($a);
   echo " => {$a[0]} {$a[1]} {$a[2]}\n";
}
// on PHP 5.2.6:
echo_sorted(array( "10", "1a", "2")); // => 10 1a 2
echo_sorted(array( "10", "2", "1a")); // => 1a 2 10
echo_sorted(array( "1a", "10", "2")); // => 2 10 1a
echo_sorted(array( "1a", "2", "10")); // => 1a 2 10
echo_sorted(array( "2", "10", "1a")); // => 2 10 1a
echo_sorted(array( "2", "1a", "10")); // => 10 1a 2
?>

Let's say we have a list of names, and it is not sorted.

<?php

$names = array('Amin', 'amir', 'sarah', 'Somayeh', 'armita', 'Armin');

sort($names); // simple alphabetical sort
print_r($names);
?>
Result is :
Array
(
    [0] => Amin
    [1] => Armin
    [2] => Somayeh // actually it's not sort alphabetically from here!
    [3] => amir         // comparison is based on ASCII values.
    [4] => armita
    [5] => sarah
)

If you want to sort alphabeticaly no matter it is upper or lower case:

<?php

sort($names, SORT_STRING | SORT_FLAG_CASE);
print_r($names);
?>

Result is:
Array
(
    [0] => Amin
    [1] => amir
    [2] => Armin
    [3] => armita
    [4] => sarah
    [5] => Somayeh
)

<?php 
/*
As I found the sort() function normally works as ascending order based on the following priority :
1. NULL
2. Empty 
3. Boolean FALSE 
4. String 
5. Float 
6. Int 
7. Array
8. Object 

Consider the following array: 
*/

$a = ['fruit'=> 'apple', 'A' => 10, 20, 5, 2.5, 5=>'A new value', 'last' => 'value', TRUE, NULL, "", FALSE, array(), new StdClass];
sort($a);
var_dump($a);

#The output is: 

array(13) {
  [0]=>NULL
  [1]=> string(0) ""
  [2]=>bool(false)
  [3]=>string(11) "A new value"
  [4]=>string(5) "apple"
  [5]=>string(5) "value"
  [6]=> float(2.5)
  [7]=> int(5)
  [8]=>int(10)
  [9]=>int(20)
  [10]=>array(0) { }
  [11]=> bool(true)
  [12]=>object(stdClass)#1 (0) {}
}

//Hope it will remove your confusion when you're sorting an array with mix type data. 
?>

EDIT: To the original note by "phpdotnet at m4tt dot co dot uk" 
Use array_push instead of $new_array[$k] for some reason it was 
giving me string indexes.

Simple function to sort an array by a specific key. Maintains index association.

<?php

function array_sort($array, $on, $order=SORT_ASC)
{
    $new_array = array();
    $sortable_array = array();

    if (count($array) > 0) {
        foreach ($array as $k => $v) {
            if (is_array($v)) {
                foreach ($v as $k2 => $v2) {
                    if ($k2 == $on) {
                        $sortable_array[$k] = $v2;
                    }
                }
            } else {
                $sortable_array[$k] = $v;
            }
        }

        switch ($order) {
            case SORT_ASC:
                asort($sortable_array);
            break;
            case SORT_DESC:
                arsort($sortable_array);
            break;
        }

        foreach ($sortable_array as $k => $v) {
            array_push($new_array, $array[$k]);
        }
    }

    return $new_array;
}

$people = array(
    12345 => array(
        'id' => 12345,
        'first_name' => 'Joe',
        'surname' => 'Bloggs',
        'age' => 23,
        'sex' => 'm'
    ),
    12346 => array(
        'id' => 12346,
        'first_name' => 'Adam',
        'surname' => 'Smith',
        'age' => 18,
        'sex' => 'm'
    ),
    12347 => array(
        'id' => 12347,
        'first_name' => 'Amy',
        'surname' => 'Jones',
        'age' => 21,
        'sex' => 'f'
    )
);

print_r(array_sort($people, 'age', SORT_DESC)); // Sort by oldest first
print_r(array_sort($people, 'surname', SORT_ASC)); // Sort by surname

/*
Array
(
    [12345] => Array
        (
            [id] => 12345
            [first_name] => Joe
            [surname] => Bloggs
            [age] => 23
            [sex] => m
        )

    [12347] => Array
        (
            [id] => 12347
            [first_name] => Amy
            [surname] => Jones
            [age] => 21
            [sex] => f
        )

    [12346] => Array
        (
            [id] => 12346
            [first_name] => Adam
            [surname] => Smith
            [age] => 18
            [sex] => m
        )

)
Array
(
    [12345] => Array
        (
            [id] => 12345
            [first_name] => Joe
            [surname] => Bloggs
            [age] => 23
            [sex] => m
        )

    [12347] => Array
        (
            [id] => 12347
            [first_name] => Amy
            [surname] => Jones
            [age] => 21
            [sex] => f
        )

    [12346] => Array
        (
            [id] => 12346
            [first_name] => Adam
            [surname] => Smith
            [age] => 18
            [sex] => m
        )

)
*/

?>

If you need to sort an array containing some equivalent values and you want the equivalents to end up next to each other in the overall order (similar to a MySQL's ORDER BY output), rather than breaking the function, do this:

<?php

sort($array, ksort($array))

?>

-When the sort() function finds two equivalents, it will sort them arbitrarily by their key #'s as a second parameter.

-Dirk

sort() used with strings doesn't sort just alphabetically. It sorts all upper-case strings alphabetically first and then sorts lower-case strings alphabetically second. 
Just in case anyone was as confused as I was and I've never seen this mentioned anywhere.

This function will sort entity letters eg:é

I hope that help someone

function sort_entity($array) {
    $total = count($array);
    for ($i=0;$i<$total;$i++) {
        if ($array[$i]{0} == '&') {
            $array[$i] = $array[$i]{1}.$array[$i];
        } else {
            $array[$i] = $array[$i]{0}.$array[$i];
        }
    }
    sort($array);
    
    for ($i=0;$i<$total;$i++) {
        $array[$i] = substr($array[$i],1);
    }
    
    return $array;
}

This took me longer than it should have to figure out, but if you want the behavior of sort($array, SORT_STRING) (that is, re-indexing the array unlike natcasesort) in a case-insensitive manner, it is a simple matter of doing usort($array, strcasecmp).

Commenting on note http://www.php.net/manual/en/function.sort.php#62311 :

Sorting an array of objects will not always yield the results you desire.

As pointed out correctly in the note above, sort() sorts the array by value of the first member variable. However, you can not always assume the order of your member variables! You must take into account your class hierarchy!

By default, PHP places the inherited member variables on top, meaning your first member variable is NOT the first variable in your class definition! 
However, if you use code analyzers or a compile cache, things can be very different. E.g., in eAccelerator, the inherited member variables are at the end, meaning you get different sort results with caching on or off.

Conclusion:
Never use sort on arrays with values of a type other than scalar or array.

In order to make some multidimensional quick sort implementation, take advantage of this stuff

<?php
        function quickSortMultiDimensional($array, $chave) {
            if( count( $array ) < 2 ) {
                return $array;
            }
            $left = $right = array( );
            reset( $array );
            $pivot_key    = key( $array );
            $pivot    = array_shift( $array );
            foreach( $array as $k => $v ) {
                if( $v[$chave] < $pivot[$chave] )
                        $left[$k][$chave] = $v[$chave];
                else
                        $right[$k][$chave] = $v[$chave];
            }
            return array_merge(
                                    quickSortMultiDimensional($left, $chave), 
                                    array($pivot_key => $pivot), 
                                    quickSortMultiDimensional($right, $chave)
            );            
        }
?>

I make it using the idea from pageconfig dot com

tks for viewing

I ran into the same problem with case insensitive sorting. Actually I think there should be a SORT_STRING_CASE flag but I tried the following:

usort($listing, 'strcasecmp');

This didn't work (why not?), but you can do a proper case insensitive sort like this:

usort($listing, create_function('$a,$b','return strcasecmp($a,$b);'));

Here is no word about sorting UTF-8 strings by any collation. This should not be so uncommon?

Sorting the keys, but keep the values in order is not possible by just ordering, because it would result in a new array. This is also the solution: Create a new array

<?php
$a = array(9=>"a",8=>"c",5=>"d");

$keys = array_keys($a);
sort($keys);
$result = array_combine($keys, array_values($a));

//Result : array(5=>"a",8=>"c",9=>"d");
?>

As some people have mentioned before sorting a multidimentional array can be a bit tricky. it took me quite a while to get it going but it works as a charm:

<?php
//$order has to be either asc or desc
 function sortmulti ($array, $index, $order, $natsort=FALSE, $case_sensitive=FALSE) {
        if(is_array($array) && count($array)>0) {
            foreach(array_keys($array) as $key) 
            $temp[$key]=$array[$key][$index];
            if(!$natsort) {
                if ($order=='asc')
                    asort($temp);
                else    
                    arsort($temp);
            }
            else 
            {
                if ($case_sensitive===true)
                    natsort($temp);
                else
                    natcasesort($temp);
            if($order!='asc') 
                $temp=array_reverse($temp,TRUE);
            }
            foreach(array_keys($temp) as $key) 
                if (is_numeric($key))
                    $sorted[]=$array[$key];
                else    
                    $sorted[$key]=$array[$key];
            return $sorted;
        }
    return $sorted;
}
?>

I read up on various problems re: sort() and German Umlaut chars and my head was soon spinning - bug in sort() or not, solution via locale or not, etc. ... (a total newbie here).

The obvious solution for me was quick and dirty: transform the Umlaut chars (present as HTML codes in my case) to their normal equivalent ('ä' = 'ae', 'ö' = 'oe', 'ü' = 'ue', 'ß' = 'ss' etc.), sort the array, then transform back. However there are cases in which a 'Mueller' is really that and does NOT need to be transformed into 'Müller' afterwards. Hence I for example replace the Umlaut itself with it's normal equivalent plus a char not used in the string otherwise (e.g. '_') so that the transfer back to Umlaut would only take place on certain combinations.

Of course any other char instead of '_' can be used as additional char (influencing the sort result). I know that my solution is rough at the edges and may cause other sort problems but it was sufficient for my purpose.

The array '$dat' in this example was filled with German town names (I actually worked with a multiple array ('$dat[][]') but stripped the code down to this as it's easier to understand):

<?php
// START Pre-sorting (Umlaut -> normal letters)
$max = count($dat);
for($totcnt = 0; $totcnt < $max; $totcnt++){
   $dat[$totcnt]=str_replace('&szlig;','ss_',$dat[$totcnt]);
   $dat[$totcnt]=str_replace('&Auml;','Ae_',$dat[$totcnt]);
   $dat[$totcnt]=str_replace('&auml;','ae_',$dat[$totcnt]);
   $dat[$totcnt]=str_replace('&Ouml;','Oe_',$dat[$totcnt]);
   $dat[$totcnt]=str_replace('&ouml;','oe_',$dat[$totcnt]);
   $dat[$totcnt]=str_replace(