While this may seem obvious, user-defined array sorting functions ( uksort(), uasort(), usort() ) will *not* be called if the array does not have *at least two values in it*.
The following code:
<?php
function usortTest($a, $b) {
var_dump($a);
var_dump($b);
return -1;
}
$test = array('val1');
usort($test, "usortTest");
$test2 = array('val2', 'val3');
usort($test2, "usortTest");
?>
Will output:
string(4) "val3"
string(4) "val2"
The first array doesn't get sent to the function.
Please, under no circumstance, place any logic that modifies values, or applies non-sorting business logic in these functions as they will not always be executed.
Sorting Arrays
PHP has several functions that deal with sorting arrays, and this document exists to help sort it all out.
The main differences are:
- Some sort based on the array keys, whereas others by the values: $array['key'] = 'value';
- Whether or not the correlation between the keys and values are maintained after the sort, which may mean the keys are reset numerically (0,1,2 ...)
- The order of the sort: alphabetical, low to high (ascending), high to low (descending), numerical, natural, random, or user defined
- Note: All of these sort functions act directly on the array variable itself, as opposed to returning a new sorted array
- If any of these sort functions evaluates two members as equal then the order is undefined (the sorting is not stable).
| Function name | Sorts by | Maintains key association | Order of sort | Related functions |
|---|---|---|---|---|
| array_multisort() | value | associative yes, numeric no | first array or sort options | array_walk() |
| asort() | value | yes | low to high | arsort() |
| arsort() | value | yes | high to low | asort() |
| krsort() | key | yes | high to low | ksort() |
| ksort() | key | yes | low to high | asort() |
| natcasesort() | value | yes | natural, case insensitive | natsort() |
| natsort() | value | yes | natural | natcasesort() |
| rsort() | value | no | high to low | sort() |
| shuffle() | value | no | random | array_rand() |
| sort() | value | no | low to high | rsort() |
| uasort() | value | yes | user defined | uksort() |
| uksort() | key | yes | user defined | uasort() |
| usort() | value | no | user defined | uasort() |
add a note
User Contributed Notes 8 notes
"Matthew Rice" ¶
6 years ago
oculiz at gmail dot com ¶
8 years ago
Another way to do a case case-insensitive sort by key would simply be:
<?php
uksort($array, 'strcasecmp');
?>
Since strcasecmp is already predefined in php it saves you the trouble to actually write the comparison function yourself.
Hayley Watson ¶
3 years ago
Stabilizing the sort functions (in this case, usort).
<?php
function stable_usort(&$array, $cmp)
{
$i = 0;
$array = array_map(function($elt)use(&$i)
{
return [$i++, $elt];
}, $array);
usort($array, function($a, $b)use($cmp)
{
return $cmp($a[1], $b[1]) ?: ($a[0] - $b[0]);
});
$array = array_column($array, 1);
}
?>
Tags each array element with its original position in the array so that when the comparison function returns 0 the tie can be broken to put the earlier element first.
roger dot vermeir at nokia dot com ¶
2 months ago
I tend to use the following code for adding a sort on the keys when different values have the same key:
<?php
$arr = array();
$res = $db->query("some sql");
while ($row = $res->fetchRow()) {
$key = trim($row[0]); // I know... 'colname' is better
$value = trim($row[1]);
$arr[$key] = $value . "_" . sprintf('%09d', $key); // number
}
arsort($arr);
foreach ($arr as $key=>$value_and_key) {
list($value, $dummykey) = explode("_", $value_and_key);
echo "$key and $value"; // reverse sorted by value, then key
}
?>
Appending the key to the value makes arsort a kind of dual sort.
No need for extra user-defined functions...
Roger Vermeir
luca at lauretta dot info ¶
1 year ago
If you're looking for a quick solution to make usort stable, you could use uksort like in the following example:
<?php
uksort($array, function ($ak, $bk) use ($array) {
$a = $array[$ak];
$b = $array[$bk];
if ($a['foo'] === $b['foo']) return $ak - $bk;
return $a['foo'] > $b['foo'] ? 1 : -1;
});
?>
This works as expected only if the initial indices (keys) of $array are in ascending order.
bizarrus at icloud dot com ¶
1 year ago
If you wan't to sort JSON based data or an multidimensional object (ascending or descending), you must fetch the array/object keys for sorting - After a sort, you can build a new Object with the correct sorting.
**Example Data:**
<?php
$json = [
'nameZ' => [
'A' => true,
'F' => true,
'K' => true
],
'nameU' => 'Hello World!',
'nameA' => [
'subData' => [
'resultX' => 1,
'resultB' => 4,
'resultI' => 6
]
],
'nameK' => [
'testing' => true
],
];
?>
**Function:**
<?php
function json_sort(&$json, $ascending = true) {
$names = [];
// Creating a named array for sorting
foreach($json AS $name => $value) {
$names[] = $name;
}
if($ascending) {
asort($names);
} else {
arsort($names);
}
$result = [];
foreach($names AS $index => $name) {
// Sorting Sub-Data
if(is_array($json[$name]) || is_object($json[$name])) {
json_sort($json[$name], $ascending);
}
$result[$name] = $json[$name];
}
$json = $result;
}
?>
**Usage:**
<?php
json_sort($json, true); // Ascending order
print_r($json);
?>
or
<?php
json_sort($json, false); // Descending order
print_r($json);
?>
I had written these method for generating HashValues for an API-Request. The HTTP-Request POST the JSON-Data as Body and over GET-Parameter, an digest/token will be appended to validate the JSON-Data (prevent manipulation of the JSON Data).
monicse09ku at yahoo dot com ¶
4 years ago
// takes an array and desired key value and returns an array
// searches through an array for a given key, if found the key that row is made the first row and the other rows are inserted accordingly.
// the facility of this function is to get the value with a specific key of an array as the first value.
/////////////////////////////// function starts //////////////////////////////
function dksort($array, $case){
if(array_key_exists($case,$array)){
$a[$case] = $array[$case];
foreach($array as $key=>$val){
if($case==$key){
}else{
$a[$key] = $array[$key];
}
}
}
return $a;
}
$d = array(
'22'=>'jdfhgjfd',
'33'=>'jdfhgjfd',
'11'=>'jrtyrjfd',
'55'=>'jrtydairjfd',
'77'=>'jopo',
'99'=>'jrtasajfd',
'44'=>'jopasdwo',
'88'=>'hdgatyuyuiuy'
);
$c = dksort($d, '55');
print_r($c);
////////////////////////// function ends ////////////////////////////////////////
Mssler ¶
4 years ago
simple example sorting dotted version numbers
function sortByVersionnumber($a,$b){
$ta=explode(".",$a); $tb=explode(".",$b);
foreach ($ta as $k => $v){
if (isset($tb[$k])){
if($ta[$k] > $tb[$k]) {
return 1;
} elseif($ta[$k] < $tb[$k]) {
return -1;
}
}
}
return 0;
}
function vnksort(&$array){
uksort($array ,"sortByVersionnumber");
}
