As the documentation says, the comparison function needs to return an integer that is either "less than, equal to, or greater than zero". There is no requirement to restrict the value returned to -1, 0, 1.
<?php
usort($array, function($a, $b) {
if($a->integer_property > $b->integer_property) {
return 1;
}
elseif($a->integer_property < $b->integer_property) {
return -1;
}
else {
return 0;
}
});
?>
can be simplified to
<?php
usort($array, function($a, $b) {
return $a->integer_property - $b->integer_property;
});
?>
This of course applies to any comparison function that calculates an integer "score" for each of its arguments to decide which is "greater".
usort
(PHP 4, PHP 5, PHP 7)
usort — Sort an array by values using a user-defined comparison function
Descrierea
This function will sort an array by its values using a user-supplied comparison function. If the array you wish to sort needs to be sorted by some non-trivial criteria, you should use this function.
Notă:
Dacă în rezultatul comparației doi membri sunt egali, ordinea lor relativă în tabloul sortat nu este definită.
Notă: Această funcție atribuie chei noi elementelor din
array. Ea va elimina cheile existente, care posibil au fost atribuite, în loc doar să rearanjeze cheile.
Parametri
-
array -
The input array.
-
callback -
Funcția de comparare trebuie să întoarcă un întreg mai mic, egal cu sau mai mare decât zero dacă primul argument este considerat respectiv mai mic, egal cu sau mai mare decât al doilea argument. Notă: înainte de PHP 7.0.0 acest întreg trebuia să fie cuprins în domeniul de la -2147483648 până la 2147483647.
PrecauţieReturning non-integer values from the comparison function, such as float, will result in an internal cast to int of the callback's return value. So values such as 0.99 and 0.1 will both be cast to an integer value of 0, which will compare such values as equal.
Valorile întoarse
Întoarce valoarea true în cazul
succesului sau false în cazul eșecului.
Exemple
Example #1 usort() example
<?php
function cmp($a, $b)
{
if ($a == $b) {
return 0;
}
return ($a < $b) ? -1 : 1;
}
$a = array(3, 2, 5, 6, 1);
usort($a, "cmp");
foreach ($a as $key => $value) {
echo "$key: $value\n";
}
?>
Exemplul de mai sus va afișa:
0: 1 1: 2 2: 3 3: 5 4: 6
Notă:
Obviously in this trivial case the sort() function would be more appropriate.
Example #2 usort() example using multi-dimensional array
<?php
function cmp($a, $b)
{
return strcmp($a["fruit"], $b["fruit"]);
}
$fruits[0]["fruit"] = "lemons";
$fruits[1]["fruit"] = "apples";
$fruits[2]["fruit"] = "grapes";
usort($fruits, "cmp");
while (list($key, $value) = each($fruits)) {
echo "\$fruits[$key]: " . $value["fruit"] . "\n";
}
?>
When sorting a multi-dimensional array, $a and $b contain references to the first index of the array.
Exemplul de mai sus va afișa:
$fruits[0]: apples $fruits[1]: grapes $fruits[2]: lemons
Example #3 usort() example using a member function of an object
<?php
class TestObj {
var $name;
function TestObj($name)
{
$this->name = $name;
}
/* This is the static comparing function: */
static function cmp_obj($a, $b)
{
$al = strtolower($a->name);
$bl = strtolower($b->name);
if ($al == $bl) {
return 0;
}
return ($al > $bl) ? +1 : -1;
}
}
$a[] = new TestObj("c");
$a[] = new TestObj("b");
$a[] = new TestObj("d");
usort($a, array("TestObj", "cmp_obj"));
foreach ($a as $item) {
echo $item->name . "\n";
}
?>
Exemplul de mai sus va afișa:
b c d
Example #4 usort() example using a closure to sort a multi-dimensional array
<?php
$array[0] = array('key_a' => 'z', 'key_b' => 'c');
$array[1] = array('key_a' => 'x', 'key_b' => 'b');
$array[2] = array('key_a' => 'y', 'key_b' => 'a');
function build_sorter($key) {
return function ($a, $b) use ($key) {
return strnatcmp($a[$key], $b[$key]);
};
}
usort($array, build_sorter('key_b'));
foreach ($array as $item) {
echo $item['key_a'] . ', ' . $item['key_b'] . "\n";
}
?>
Exemplul de mai sus va afișa:
y, a x, b z, c
A se vedea și
- uasort() - Sort an array with a user-defined comparison function and maintain index association
- Comparația funcțiilor de sortare a tablourilor
add a note
User Contributed Notes 10 notes
Hayley Watson ¶
11 years ago
luke dot semerau at gmail dot com ¶
15 years ago
If you need to use usort with a key in the calling method, I wrote this as a utility:
<?php
function usort_comparison($obj, $method, $key) {
$usorter = &new Usort($obj, $method, $key);
return array($usorter, "sort");
}
class Usort {
function __construct($obj, $method, $key) {
$this->obj = $obj;
$this->method = $method;
$this->key = $key;
}
function sort($a, $b) {
return call_user_func_array(array($this->obj, $this->method), array($a, $b, $this->key));
}
}
?>
<?php
require_once("util/usort.php");
class Foo {
$items = array(FooBar(13), FooBar(2));
public function sorter() {
usort($this-items, usort_comparison("Foo", "_cmp", "item"));
}
public static function _cmp($a, $b, $key) {
return strcasecmp($a->$key, $b->$key);
}
}
class FooBar {
public $item;
function __construct($val) {
$this->item = $val;
}
}
?>
~ simple example... but in the way I need to use it was the key was used in a switch statement to choose the different member of the object to compare against dynamically (as in, sort by x or y or z)
mkr at binarywerks dot dk ¶
21 years ago
If you want to sort an array according to another array acting as a priority list, you can use this function.
<?php
function listcmp($a, $b)
{
global $order;
foreach($order as $key => $value)
{
if($a==$value)
{
return 0;
break;
}
if($b==$value)
{
return 1;
break;
}
}
}
$order[0] = "first";
$order[1] = "second";
$order[2] = "third";
$array[0] = "second";
$array[1] = "first";
$array[2] = "third";
$array[3] = "fourth";
$array[4] = "second";
$array[5] = "first";
$array[6] = "second";
usort($array, "listcmp");
print_r($array);
?>
sydney at totoche dot org ¶
18 years ago
Instead of doing :
<?php $strc = strcmp( strtolower($a[$f]), strtolower($b[$f]) ); ?>
you could do this :
<?php $strc = strcasecmp( $a[$f], $b[$f] ); ?>
which is more efficient and is does case insensitive comparison according to the current locale.
derek at luddite dot net ¶
23 years ago
Needed a date sort and I didn't know if one was available so I wrote one. Maybe it'll help someone:
<?php
function DateSort($a,$b,$d="-") {
if ($a == $b) {
return 0;
} else { //Convert into dates and compare
list($am,$ad,$ay)=split($d,$a);
list($bm,$bd,$by)=split($d,$b);
if (mktime(0,0,0,$am,$ad,$ay) < mktime(0,0,0,$bm,$bd,$by)) {
return -1;
} else {
return 1;
}
}
}
?>
$d is the delimeter
gus dot antoniassi at gmail dot com ¶
4 years ago
This is a simple way to sort based on a "priority list":
<?php
$order = [1,3,0,2];
$arr = [
[ 'id' => 0 ],
[ 'id' => 1 ],
[ 'id' => 2 ],
[ 'id' => 3 ],
];
uasort(
$arr,
function ($a, $b) use ($order) {
return array_search($a['id'], $order) <=> array_search($b['id'], $order);
}
);
print_r($arr);
?>
This will return:
Array
(
[1] => Array
(
[id] => 1
)
[3] => Array
(
[id] => 3
)
[0] => Array
(
[id] => 0
)
[2] => Array
(
[id] => 2
)
)
Note that if you have a value in $arr that is not on the $order list, you will need additional checks since the array_search function returns FALSE for undefined indexes.
chris at candm dot org dot uk ¶
5 years ago
In case anyone is interested, comparative timings over 100000000 runs
Based on comparing integers (500 and 501)
Spaceship:4
()?: operator:10
Subtraction:2
Based on comparing floats (500.1 and 501.3) (caveats noted)
Spaceship:5
()?: operator:9
Subtraction:3
Based on comparing strings ("five" and "four")
Spaceship:7
()?: operator:17
(Subtraction obviously not available)
Note: a dummy run was done with an empty loop and the elapsed time for this was subtracted from each of the above times so that they reflect ONLY the time to do the comparisons. As for significance. unless you are doing very large numbers of comparisons where spaceships are the order of the day, the difference is insignificant.
inigo dot grimbergen at gmail dot com ¶
7 years ago
to sort with numeric and empty values and have the smallest on top:
<?php
usort($list, function($a, $b) {
if( $a == null && $b != null ) return 1;
if( $a != null && $b == null ) return -1;
return $a > $b ? 1 : -1;
});
?>
returns
1
2
3
null
null
null
andi_mclean at ntlworld dot com ¶
12 years ago
I needed a sort method that would sort strings but take note of any numbers and would compare them as number. I also want to ignore any non alphanumerical characters.
Eg.
Slot 1 Example
Slot 10 Example
Slot 2 Example
Should infact be
Slot 1 Example
Slot 2 Example
Slot 10 Example
<?php
function sort_with_numbers($a , $b) {
$a = explode(' ',$a);
$b = explode(' ',$b);
$size = min(count($a), count($b));
for($index =0; $index < $size; ++$index) {
$a1 = ereg_replace("[^A-Za-z0-9]", "",$a[$index]);
$b1 = ereg_replace("[^A-Za-z0-9]", "",$b[$index]);
$equal = 0;
if (is_numeric($a1) && is_numeric($b1)) {
$equal = $a1 - $b1;
} else {
$equal = strcasecmp($a1,$b1);
}
if ($equal < 0) {
return -1;
}
if ($equal > 0) {
return 1;
}
}
return count($a) - count($b);
}
?>
bo at erichsen dot com ¶
23 years ago
when using usort to refer to a function inside a class i have succesfully used:
<?php usort($myarray,array($this,"cmp")); ?>
