Sort array by the value of the key - php

Question

i'm trying to sort an array by the value of a sub-key in DESC order but I'm stuck.
I've could make it with ksort but it was in ascending order..
Here's my array :
array_by_lang => array(
[no] => array(
[3-1] => array(//some informations),
[3-10] => array(//informations),
[3-7] => array(//informations),
[5-1] => array(//informations)
)
)
what i want to obtain is something like :
array_by_lang => array(
[no] => array(
[5-1] => array(//informations),
[3-10] => array(//some informations),
[3-7] => array(//informations),
[3-1] => array(//informations)
)
)
Is that possible ? Thanks a lot

Answer 1

I think, you need "reversing natural sort by key". Just with array_multisort and array_reverse (see also natsort):
$array_by_lang = array(
'no' => array(
'3-1' => array('info_1'),
'3-10' => array('info_2'),
'3-7' => array('info_3'),
'5-1' => array('info_4'),
)
);
array_multisort(array_keys($array_by_lang['no']),SORT_NATURAL, $array_by_lang['no']);
$array_by_lang['no'] = array_reverse($array_by_lang['no']); // reverse natural order - "DESC"
var_dump($array_by_lang);
Output
array(1) {
["no"]=>
array(4) {
["5-1"]=>
array(1) {
[0]=>
string(6) "info_4"
}
["3-10"]=>
array(1) {
[0]=>
string(6) "info_2"
}
["3-7"]=>
array(1) {
[0]=>
string(6) "info_3"
}
["3-1"]=>
array(1) {
[0]=>
string(6) "info_1"
}
}
}

Answer 2

This might help -
$a = array(
'3-1' => array('//some informations'),
'3-10' => array('//informations'),
'3-7' => array('//informations'),
'5-1' => array('//informations')
);
## Array for keys
$temp= array();
foreach(array_keys($a) as $v) {
$t = explode('-', $v);
$temp[$t[0]][] = $t[1];
}
## Sort the keys
foreach($temp as &$ar) {
rsort($ar);
}
krsort($temp);
## Final array
$final= array();
foreach($temp as $k => $f) {
foreach($f as $v) {
$key = $k . '-' . $v;
$final[$key] = $a[$key];
}
}
var_dump($final);
Output
array(4) {
["5-1"]=>
array(1) {
[0]=>
string(14) "//informations"
}
["3-10"]=>
array(1) {
[0]=>
string(14) "//informations"
}
["3-7"]=>
array(1) {
[0]=>
string(14) "//informations"
}
["3-1"]=>
array(1) {
[0]=>
string(19) "//some informations"
}
}
DEMO