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