array_map

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

array_mapApplies the callback to the elements of the given arrays

설명

array array_map ( callable $callback , array $array1 [, array $... ] )

array_map() returns an array containing all the elements of array1 after applying the callback function to each one. The number of parameters that the callback function accepts should match the number of arrays passed to the array_map()

인수

callback

Callback function to run for each element in each array.

array1

An array to run through the callback function.

...

Variable list of array arguments to run through the callback function.

반환값

Returns an array containing all the elements of array1 after applying the callback function to each one.

예제

Example #1 array_map() example

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

$a = array(12345);
$b array_map("cube"$a);
print_r($b);
?>

This makes $b have:

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

Example #2 array_map() using a lambda function (as of PHP 5.3.0)

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

print_r(array_map($funcrange(15)));
?>
Array
(
    [0] => 2
    [1] => 4
    [2] => 6
    [3] => 8
    [4] => 10
)

Example #3 array_map() - using more arrays

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

function 
map_Spanish($n$m)
{
    return(array(
$n => $m));
}

$a = array(12345);
$b = array("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);
?>

위 예제의 출력:

// printout of $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
)

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

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

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

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

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

)

Usually when using two or more arrays, they should be of equal length because the callback function is applied in parallel to the corresponding elements. If the arrays are of unequal length, shorter ones will be extended with empty elements to match the length of the longest.

An interesting use of this function is to construct an array of arrays, which can be easily performed by using NULL as the name of the callback function

Example #4 Creating an array of arrays

<?php
$a 
= array(12345);
$b = array("one""two""three""four""five");
$c = array("uno""dos""tres""cuatro""cinco");

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

위 예제의 출력:

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
        )

)

The returned array will preserve the keys of the array argument if and only if exactly one array is passed. If more than one array is passed, the returned array will have sequential integer keys.

Example #5 array_map() - with string keys

<?php
$arr 
= array("stringkey" => "value");
function 
cb1($a) {
    return array (
$a);
}
function 
cb2($a$b) {
    return array (
$a$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));
?>

위 예제의 출력:

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"
  }
}

참고

  • array_filter() - 콜백 함수를 사용하여 배열 원소를 필터
  • array_reduce() - 콜백 함수를 사용하여 배열을 반복적으로 단일 값으로 축소
  • array_walk() - 배열의 각 원소에 대해서 특정 함수를 적용
  • callback형에 대한 정보

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User Contributed Notes 6 notes

up
14
lukasz dot mordawski at gmail dot com
8 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 $this inside anonymous function (unlike for example javascript) is the instance of MyFilterClass inside which we called it.
I hope this would be useful for anyone.
up
13
elfe1021 at gmail dot com
8 years ago
Find an interesting thing that in array_map's callable function, late static binding does not work:
<?php
class A {
    public static function
foo($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
6 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
13 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
13 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
8 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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