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() 返回一个 array,内容为 array
的元素按相应的顺序调用
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 callback
函数处理之后 array
(有多个数组时,为 arrays
) 对应索引所有元素作为函数的参数。
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 。
|
范例
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);
?>
以上例程会输出:
// 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);
?>
以上例程会输出:
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));
?>
以上例程会输出:
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));
?>
以上例程会输出:
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);
?>
以上例程会输出:
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
User Contributed Notes 8 notes
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 $this inside anonymous function (unlike for example javascript) is the instance of MyFilterClass inside which we called it.
I hope this would be useful for anyone.
Find an interesting thing that in array_map's callable function, late static binding does not work:
<?php
class A {
public static function foo($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)
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']; }, $data));
?>
It's not necessarily better than a for/foreach loop, but the occasional one-liner for trivial tasks can help keep your code cleaner.
To transpose rectangular two-dimension array, use the following code:
array_unshift($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
)
)
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.
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;
}
?>
/**
* Function which recursively applies a callback to all values and also its
* keys, and returns the resulting array copy with the updated keys and
* values.
* PHP's built-in function array_walk_recursive() only applies the passed
* callback to the array values, not the keys, so this function simply applies
* the callback to the keys too (hence the need of working with a copy,
* as also updating the keys would lead to reference loss of the original
* array). I needed something like this, hence my idea of sharing it here.
*
* @param callable $func callback which takes one parameter (value
* or key to be updated) and returns its
* updated value
*
* @param array $arr array of which keys and values shall be
* get updated
*/
function array_map_recursive(
callable $func,
array $arr
) {
// Initiate copied array which will hold all updated keys + values
$result = [];
// Iterate through the key-value pairs of the array
foreach ( $arr as $key => $value ) {
// Apply the callback to the key to create the updated key value
$updated_key = $func( $key );
// If the iterated value is not an array, that means we have reached the
// deepest array level for the iterated key, so in that case, assign
// the updated value to the updated key value in the final output array
if ( ! is_array( $value ) ) {
$result[$updated_key] = $func( $value );
} else {
// If the iterated value is an array, call the function recursively,
// By taking the currently iterated value as the $arr argument
$result[$updated_key] = array_map_recursive(
$func,
$arr[$key]
);
}
} // end of iteration through k-v pairs
// And at the very end, return the generated result set
return $result;
} // end of array_map_recursive() function definition
A general solution for the problem of wanting to know the keys in the callback, and/or retain the key association in the returned array:
<?php
/**
* Like array_map() but callback also gets passed the current key as the
* first argument like so:
* function($key, $val, ...$vals) { ... }
* ...and returned array always maintains key association, even if multiple
* array arguments are passed.
*/
function array_map_assoc(callable $callback, array $array, array ...$arrays) {
$keys = array_keys($array);
array_unshift($arrays, $keys, $array);
return array_combine($keys, array_map($callback, ...$arrays));
}
?>
Because it uses array_map() directly, it behaves the same way in regard to ignoring the keys of subsequent array arguments. It also has the same variadic signature.