PHP Arrays sort

There are lots of PHP defined function to order arrays (the core of PHP, technically are hashmaps), ordering by value or keys, preserving key order or not, using an user-defined function, normal or reverse order, etc...

Following, some clear example of the main ones, and some tips about how to remember them

ORDER BY VALUE

sort(): order by VALUE (keys destroyed and renumberted starting from zero)
$a = array('z'=>'A', 'y'=>'C','k'=>'B','x'=>'B');
sort( $a ); # Array ( A ,B ,B ,C )

asort(): as the previous, but it maintains index association
$a = array('z'=>'A', 'y'=>'C','k'=>'B','x'=>'B');
asort( $a ); # Array ( [z] => A , [k] => B , [x] => B , [y] => C )

natsort(): use "natural" sorting
$a = array('z'=>'5p', 'y'=>'10p','20p');
sort( $a ); # Array ( 10p ,20p ,5p )
natsort( $a ); # Array ( [2] => 5p , [0] => 10p , [1] => 20p )

ORDER BY KEY

ksort(): order by key (maintaining associations)
$a = array('z'=>'A', 'y'=>'C','k'=>'B','x'=>'B');
ksort( $a ); # Array ( [k] => B , [x] => B , [y] => C , [z] => A )

USER-DEFINED COMPARISON FUNCTION

usort(): compare using an user-defined function. (keys destroyed and renumbered starting from zero)
$a = array( '0'=>array('id'=>4,'n'=>'aaa') , '1'=>array('id'=>2,'n'=>'bbb'), '2'=>array('id'=>1,'n'=>'ccc'), );
usort($a, function ($a, $b) { #order by '[id]' contained in the elements #closure (php 5.3)
return ($a['id'] < $b['id']) ? -1 : 1; }); #Array ( Array ( [id] => 1 [n] => ccc ) ,Array ( [id] => 2 [n] => bbb ) ,Array ( [id] => 4 [n] => aaa ) )

uasort(): as usort but MAINTAINS the KEYS

HOW TO REMEMBER FUNCTION NAMES

sort = default sort behaviour: order by value and destroy keys
If the function name contains:
u = sort using [U]ser-defined function (Usort, Uasort, Uksort)
a = [A]ssociative: maintains key order (Asort, Arsort, uAsort)
k = order by [K]ey (Ksort, Krsort)
r = [R]everse order (aRsort, kRsort, Rsort)

OTHER ARRAY USEFUL FUNCTIONS

shuffle(): scramble array s contents. (keys destroyed and renumberted starting from 0)

array_rand($array, $number): return $number random elements from $array

array_multisort()

array_shift( array &$array ) ; return the array shifted by 1element off the beginning of array (remove the 1st)

array_slice( array $array , 3, 2, $preserve_keys); RETURNS 2 elements starting from the 4th. if $preserve_keys is true, the keys in the return array are the same in the original one
$a = array(0=>1, 1=>2, 2=>3, 4=>4, 3=>5, 5=>6);
$a = array_slice($a,3,2); #Array ( 4 ,5 )

array_splice(): remove the slice (REFERENCE) and return the removed part
$a = array(1, 2, 3, 4, 5, 6);
$returned = array_splice($a,3,2); #remove 2 elements from 4th elem. return the removed slice
# $returned = Array ( 4 ,5 )
# $a = Array ( 1 ,2 , 3 , 6 )