rsort() – Where it resets key associations as well.
arsort() – Where it sorts in descending order, while keeping the key associations as well.

The main difference is that sort() will sort an array without concerning it’s key associations while asort() will maintain it’s key association as well.

$array = array(‘a’=>’foo’,'b’=>’bar’,'c’=>’baz’);
asort($array);
print_r($array);

Array
(
[b] => bar
=> baz
[a] => foo
)

<?php
function setcase(&$value, &$key){
$value = strtoupper($value);
}
$type = array('internal','external');
$format[] = array('rss','html','xml');
$format[] = array('csv','jason');
$map = array_combine($type, $format);
array_walk_recursive($map, 'setcase');
print_r($map);
?>

Only scalar values will be converted to upper cases. ‘ internal’ and ‘external’ are not passed into the user defined function.

Array
(
    [internal] => Array
        (
            [0] => RSS
            [1] => HTML
            [2] => XML
        )

    [external] => Array
        (
            [0] => CSV
            [1] => JASON
        )

)

print_r() or var_dump()

Yes it does.

count() or sizeof()

is_array() function can be used.

array_key_exist or isset() methods can be used.

array_key_exists()
It is because isset returns false even though if an array element is defined as a NULL.

array_flip just flip the values of the array with its key values. But array_reverse actually reverse the order of the array’s elements, so that last one appears first.