usort

(PHP 4, PHP 5, PHP 7, PHP 8)

usort — 使用用户自定义的比较函数对数组中的值进行排序

说明

usort(array &$array, callable $callback): true

根据用户提供的比较函数，对 array 原地排序。

注意:
如果两个成员完全相同，那么它们将保持原来的顺序。在 PHP 8.0.0 之前，它们在排序数组中的相对顺序是未定义的。

注意: 此函数为 array 中的元素赋与新的键名。这将删除原有的键名，而不是仅仅将键名重新排序。

参数

array: 输入的数组
callback: 在第一个参数小于，等于或大于第二个参数时，该比较函数必须相应地返回一个小于，等于或大于 0 的整数。

callback(mixed $a, mixed $b): int

警告
从比较函数中返回非整数值，例如 float，将导致内部强制转换为 callback 返回值为 int。因此，诸如 0.99 和 0.1 之类的值都将被转换为整数值 0，将这些值比较的话将会是相等。

返回值

总是返回 true。

更新日志

版本	说明
8.2.0	现在返回类型为 `true`；之前是 bool。
8.0.0	如果 `callback` 接受引用传递参数，该方法将会抛出 `E_WARNING`。

示例

示例 #1 usort() 示例

<?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";
}
?>

以上示例会输出：

0: 1
1: 2
2: 3
3: 5
4: 6

注意:
很明显在这个小例子中用 sort() 函数更合适。

示例 #2 使用多维数组的 usort() 示例

<?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");

foreach ($fruits as $key => $value) {
    echo "\$fruits[$key]: " . $value["fruit"] . "\n";
}
?>

当排序多维数组时，$a 和 $b 包含到数组第一个索引的引用。

以上示例会输出：

$fruits[0]: apples
$fruits[1]: grapes
$fruits[2]: lemons

示例 #3 使用一个对象的成员函数的 usort() 示例

<?php
class TestObj {
    private string $name;

    function __construct($name)
    {
        $this->name = $name;
    }

    /* This is the static comparing function: */
    static function cmp_obj($a, $b)
    {
        return strtolower($a->name) <=> strtolower($b->name);
    }
}

$a[] = new TestObj("c");
$a[] = new TestObj("b");
$a[] = new TestObj("d");

usort($a, [TestObj::class, "cmp_obj"]);

foreach ($a as $item) {
    echo $item->name . "\n";
}
?>

以上示例会输出：

b
c
d

示例 #4 usort() 示例，使用闭包对多维数组进行排序

<?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";
}
?>

以上示例会输出：

y, a
x, b
z, c

示例 #5 使用太空船运算符的 usort() 示例

太空船运算符允许跨多个轴直接比较复合值。下面的示例将对 $people 按姓氏排序，如果姓氏匹配，则按名字排序。

<?php
$people[0] = ['first' => 'Adam', 'last' => 'West'];
$people[1] = ['first' => 'Alec', 'last' => 'Baldwin'];
$people[2] = ['first' => 'Adam', 'last' => 'Baldwin'];

function sorter(array $a, array $b) {
    return [$a['last'], $a['first']] <=> [$b['last'], $b['first']];
}

usort($people, 'sorter');

foreach ($people as $person) {
    print $person['last'] . ', ' . $person['first'] . PHP_EOL;
}
?>

以上示例会输出：

Baldwin, Adam
Baldwin, Alec
West, Adam

参见

uasort() - 使用用户定义的比较函数对数组进行排序并保持索引关联
uksort() - 使用用户自定义的比较函数对数组中的键名进行排序
数组排序函数对比

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＋添加备注

用户贡献的备注 11 notes

down

Hayley Watson ¶

11 years ago

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".

down

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)

down

mkr at binarywerks dot dk ¶

22 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);

?>

down

derek at luddite dot net ¶

24 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

down

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.

down

gus dot antoniassi at gmail dot com ¶

5 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.

down

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

down

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);    
}
?>

down

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.

down

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")); ?>

down

rh at 20i dot com ¶

4 months ago

A sort function to sort elements by a reference order.

function sort_by_reference(array $array_to_sort, array $reference_array): array {
    usort($array_to_sort, function($a, $b) use ($reference_array) {
        $pos_a = array_search($a, $reference_array);
        $pos_b = array_search($b, $reference_array);
        return $pos_a - $pos_b;
    });

    return $array_to_sort;
}

// Example usage
$reference_array = ["one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"];
$array_to_sort = ["three", "one", "seven", "four", "ten"];

$sorted_array = sort_by_reference($array_to_sort, $reference_array);

// Print the result to verify the sorting
print_r($sorted_array);

```
Array
(
    [0] => one
    [1] => three
    [2] => four
    [3] => seven
    [4] => ten
)
```