array_map

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

array_map 为数组的每个元素应用回调函数

说明

array_map(?callable $callback, array $array, array ...$arrays): array

array_map() 返回一个 array,包含将 array 的相应值作为回调的参数顺序调用 callback 后的结果(如果提供了更多数组,还会利用 arrays 传入)。callback 函数形参的数量必须匹配 array_map() 实参中数组的数量。多余的实参数组将会被忽略。如果提供的实参数组的数量不足,将抛出 ArgumentCountError

参数

callback

回调函数 callable,应用到每个数组里的每个元素。

多个数组操作合并时,callback 可以设置为 null。 如果只提供了 array 一个数组, array_map() 会返回输入的数组。

array

数组,遍历运行 callback 函数。

arrays

额外的数组列表,每个都遍历运行 callback 函数。

返回值

返回数组,包含将 array 的相应值作为回调的参数调用 callback 函数后的结果(如果提供了更多数组,还会利用 arrays 传入)。

当仅仅传入一个数组时,返回的数组会保留传入参数的键(key)。 传入多个数组时,返回的数组键是按顺序的 integer。

更新日志

版本 说明
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 array_map() 例子

<?php
function cube($n)
{
return (
$n * $n * $n);
}

$a = [1, 2, 3, 4, 5];
$b = array_map('cube', $a);
print_r($b);
?>

这使得 $b 成为:

Array
(
    [0] => 1
    [1] => 8
    [2] => 27
    [3] => 64
    [4] => 125
)

示例 #2 array_map() 使用匿名函数

<?php
$func
= function(int $value): int {
return
$value * 2;
};

print_r(array_map($func, range(1, 5)));

// 或者从 PHP 7.4.0 起:

print_r(array_map(fn($value): int => $value * 2, range(1, 5)));

?>
Array
(
    [0] => 2
    [1] => 4
    [2] => 6
    [3] => 8
    [4] => 10
)

示例 #3 array_map():使用更多的数组

<?php
function show_Spanish(int $n, string $m): string
{
return
"The number {$n} is called {$m} in Spanish";
}

function
map_Spanish(int $n, string $m): array
{
return [
$n => $m];
}

$a = [1, 2, 3, 4, 5];
$b = ['uno', 'dos', 'tres', 'cuatro', 'cinco'];

$c = array_map('show_Spanish', $a, $b);
print_r($c);

$d = array_map('map_Spanish', $a , $b);
print_r($d);
?>

以上示例会输出:

// 打印 $c
Array
(
    [0] => The number 1 is called uno in Spanish
    [1] => The number 2 is called dos in Spanish
    [2] => The number 3 is called tres in Spanish
    [3] => The number 4 is called cuatro in Spanish
    [4] => The number 5 is called cinco in Spanish
)

// 打印 $d
Array
(
    [0] => Array
        (
            [1] => uno
        )

    [1] => Array
        (
            [2] => dos
        )

    [2] => Array
        (
            [3] => tres
        )

    [3] => Array
        (
            [4] => cuatro
        )

    [4] => Array
        (
            [5] => cinco
        )

)

传入两个及以上的数组时,它们元素数量将会相同。因为回调函数会并行地处理相互对应的元素。 如果几个数组的元素数量不一致:空元素会扩展短那个数组,直到长度和最长的数组一样。

此函数有个有趣的用法:传入 null 作为回调函数的名称,将创建多维数组(一个数组,内部包含数组。)

示例 #4 多个数组的合并操作

<?php
$a
= [1, 2, 3, 4, 5];
$b = ['one', 'two', 'three', 'four', 'five'];
$c = ['uno', 'dos', 'tres', 'cuatro', 'cinco'];

$d = array_map(null, $a, $b, $c);
print_r($d);
?>

以上示例会输出:

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => one
            [2] => uno
        )

    [1] => Array
        (
            [0] => 2
            [1] => two
            [2] => dos
        )

    [2] => Array
        (
            [0] => 3
            [1] => three
            [2] => tres
        )

    [3] => Array
        (
            [0] => 4
            [1] => four
            [2] => cuatro
        )

    [4] => Array
        (
            [0] => 5
            [1] => five
            [2] => cinco
        )

)

示例 #5 仅有 array1 时,callback 设置为 null

<?php
$array
= [1, 2, 3];
var_dump(array_map(null, $array));
?>

以上示例会输出:

array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}

示例 #6 array_map() 键(key)是 string

<?php
$arr
= array("stringkey" => "value");
function
cb1($a) {
return [
$a];
}
function
cb2($a, $b) {
return [
$a, $b];
}
var_dump(array_map('cb1', $arr));
var_dump(array_map('cb2', $arr, $arr));
var_dump(array_map(null, $arr));
var_dump(array_map(null, $arr, $arr));
?>

以上示例会输出:

array(1) {
  ["stringkey"]=>
  array(1) {
    [0]=>
    string(5) "value"
  }
}
array(1) {
  [0]=>
  array(2) {
    [0]=>
    string(5) "value"
    [1]=>
    string(5) "value"
  }
}
array(1) {
  ["stringkey"]=>
  string(5) "value"
}
array(1) {
  [0]=>
  array(2) {
    [0]=>
    string(5) "value"
    [1]=>
    string(5) "value"
  }
}

示例 #7 array_map() - 关联数组

虽然 array_map() 不能直接支持使用数组的键(key)作为输入,但可以使用 array_keys() 进行模拟。

<?php
$arr
= [
'v1' => 'First release',
'v2' => 'Second release',
'v3' => 'Third release',
];

// 注意: 在 7.4.0 之前,使用较长的语法来代替匿名函数。
$callback = fn(string $k, string $v): string => "$k was the $v";

$result = array_map($callback, array_keys($arr), array_values($arr));

var_dump($result);
?>

以上示例会输出:

array(3) {
  [0]=>
  string(24) "v1 was the First release"
  [1]=>
  string(25) "v2 was the Second release"
  [2]=>
  string(24) "v3 was the Third release"
}

参见

  • array_filter() - 使用回调函数过滤数组的元素
  • array_reduce() - 用回调函数迭代地将数组简化为单一的值
  • array_walk() - 使用用户自定义函数对数组中的每个元素做回调处理

add a note add a note

User Contributed Notes 6 notes

up
14
lukasz dot mordawski at gmail dot com
10 years ago
Let's assume we have following situation:

<?php
class MyFilterClass {
    public function
filter(array $arr) {
        return
array_map(function($value) {
            return
$this->privateFilterMethod($value);
        });
    }

    private function
privateFilterMethod($value) {
        if (
is_numeric($value)) $value++;
        else
$value .= '.';
    }
}
?>

This will work, because $this inside anonymous function (unlike for example javascript) is the instance of MyFilterClass inside which we called it.
I hope this would be useful for anyone.
up
13
elfe1021 at gmail dot com
10 years ago
Find an interesting thing that in array_map's callable function, late static binding does not work:
<?php
class A {
    public static function
foo($name) {
        return
'In A: '.$name;
    }

    public static function
test($names) {
        return
array_map(function($n) {return static::foo($n);}, $names);
    }
}

class
B extends A{
    public static function
foo($name) {
        return
'In B: '.$name;
    }
}

$result = B::test(['alice', 'bob']);
var_dump($result);
?>

the result is:
array (size=2)
  0 => string 'In A: alice' (length=11)
  1 => string 'In A: bob' (length=9)

if I change A::test to
<?php
   
public static function test($names) {
        return
array_map([get_called_class(), 'foo'], $names);
    }
?>

Then the result is as expected:
array (size=2)
  0 => string 'In B: alice' (length=11)
  1 => string 'In B: bob' (length=9)
up
12
Mahn
8 years ago
You may be looking for a method to extract values of a multidimensional array on a conditional basis (i.e. a mixture between array_map and array_filter) other than a for/foreach loop. If so, you can take advantage of the fact that 1) the callback method on array_map returns null if no explicit return value is specified (as with everything else) and 2) array_filter with no arguments removes falsy values.

So for example, provided you have:

<?php
$data
= [
    [
       
"name" => "John",
       
"smoker" => false
   
],
    [
       
"name" => "Mary",
       
"smoker" => true
   
],
    [
       
"name" => "Peter",
       
"smoker" => false
   
],
    [
       
"name" => "Tony",
       
"smoker" => true
   
]
];
?>

You can extract the names of all the non-smokers with the following one-liner:

<?php
$names
= array_filter(array_map(function($n) { if(!$n['smoker']) return $n['name']; }, $data));
?>

It's not necessarily better than a for/foreach loop, but the occasional one-liner for trivial tasks can help keep your code cleaner.
up
11
radist-hack at yandex dot ru
15 years ago
To transpose rectangular two-dimension array, use the following code:

array_unshift($array, null);
$array = call_user_func_array("array_map", $array);

If you need to rotate rectangular two-dimension array on 90 degree, add the following line before or after (depending on the rotation direction you need) the code above:
$array = array_reverse($array);

Here is example:

<?php
$a
= array(
  array(
1, 2, 3),
  array(
4, 5, 6));
array_unshift($a, null);
$a = call_user_func_array("array_map", $a);
print_r($a);
?>

Output:

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 4
        )

    [1] => Array
        (
            [0] => 2
            [1] => 5
        )

    [2] => Array
        (
            [0] => 3
            [1] => 6
        )

)
up
6
stijnleenknegt at gmail dot com
15 years ago
If you want to pass an argument like ENT_QUOTES to htmlentities, you can do the follow.

<?php
$array
= array_map( 'htmlentities' , $array, array_fill(0 , count($array) , ENT_QUOTES) );
?>

The third argument creates an equal sized array of $array filled with the parameter you want to give with your callback function.
up
4
CertaiN
10 years ago
The most memory-efficient array_map_recursive().

<?php
function array_map_recursive(callable $func, array $arr) {
   
array_walk_recursive($arr, function(&$v) use ($func) {
       
$v = $func($v);
    });
    return
$arr;
}
?>
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