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array_map

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

array_mapApplies the callback to the elements of the given arrays

Description

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

array_map() returns an array containing the results of applying the callback to the corresponding index of array (and arrays if more arrays are provided) used as arguments for the callback. The number of parameters that the callback function accepts should match the number of arrays passed to array_map(). Excess input arrays are ignored. An ArgumentCountError is thrown if an insufficient number of arguments is provided.

Parameters

callback

A callable to run for each element in each array.

null can be passed as a value to callback to perform a zip operation on multiple arrays. If only array is provided, array_map() will return the input array.

array

An array to run through the callback function.

arrays

Supplementary variable list of array arguments to run through the callback function.

Return Values

Returns an array containing the results of applying the callback function to the corresponding index of array (and arrays if more arrays are provided) used as arguments for the callback.

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.

Examples

Example #1 array_map() example

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

$a = [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

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

print_r(array_map($funcrange(15)));

// Or as of PHP 7.4.0:

print_r(array_map(fn($value): int => $value 2range(15)));

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

Example #3 array_map() - using more arrays

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

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

$a = [12345];
$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);
?>

The above example will output:

// 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 Performing a zip operation of arrays

<?php
$a 
= [12345];
$b = ['one''two''three''four''five'];
$c = ['uno''dos''tres''cuatro''cinco'];

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

The above example will output:

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
        )

)

Example #5 null callback with only array

<?php
$array 
= [123];
var_dump(array_map(null$array));
?>

The above example will output:

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

Example #6 array_map() - with string keys

<?php
$arr 
= ['stringkey' => 'value'];
function 
cb1($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));
?>

The above example will output:

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"
  }
}

Example #7 array_map() - associative arrays

While array_map() does not directly support using the array key as an input, that may be simulated using array_keys().

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

// Note: Before 7.4.0, use the longer syntax for anonymous functions instead.
$callback fn(string $kstring $v): string => "$k was the $v";

$result array_map($callbackarray_keys($arr), array_values($arr));

var_dump($result);
?>

The above example will output:

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"
}

See Also

  • array_filter() - Filters elements of an array using a callback function
  • array_reduce() - Iteratively reduce the array to a single value using a callback function
  • array_walk() - Apply a user supplied function to every member of an array

add a note add a note

User Contributed Notes 6 notes

up
14
lukasz dot mordawski at gmail dot com
7 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 $this inside anonymous function (unlike for example javascript) is the instance of MyFilterClass inside which we called it.
I hope this would be useful for anyone.
up
13
elfe1021 at gmail dot com
7 years ago
Find an interesting thing that in array_map's callable function, late static binding does not work:
<?php
class A {
    public static function
foo($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
5 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
12 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
7 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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