array_map
(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)
array_map — Applies the callback to the elements of the given arrays
Description
array_map() returns an array containing
the results of applying the callback
to the corresponding value 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.
nullcan be passed as a value tocallbackto perform a zip operation on multiple arrays. If onlyarrayis provided, array_map() will return the input array. -
array -
An array to run through the
callbackfunction. -
arrays -
Supplementary variable list of array arguments to run through the
callbackfunction.
Return Values
Returns an array containing the results of applying the callback
function to the corresponding value 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.
Changelog
| Version | Description |
|---|---|
| 8.0.0 |
If callback expects a parameter to be passed
by reference, this function will now emit an E_WARNING.
|
Examples
Example #1 array_map() example
<?php
function cube($n)
{
return ($n * $n * $n);
}
$a = [1, 2, 3, 4, 5];
$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 $value * 2;
};
print_r(array_map($func, range(1, 5)));
// Or as of PHP 7.4.0:
print_r(array_map(fn($value): int => $value * 2, range(1, 5)));
?>
Array
(
[0] => 2
[1] => 4
[2] => 6
[3] => 8
[4] => 10
)
Example #3 array_map() - using more arrays
<?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);
?>
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 = [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);
?>
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 = [1, 2, 3];
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 $k, string $v): string => "$k was the $v";
$result = array_map($callback, array_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
