(PHP 4 >= 4.0.6, PHP 5, PHP 7)
array_map — Applies the callback to the elements of the given arrays
array_map() returns an array containing
the results of applying the callback
function to the corresponding index of array1
(and ... 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().
callbackCallback function 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 array1 is provided,
array_map() will return the input array.
array1
An array to run through the callback function.
...
Supplementary variable list of array arguments to run through the
callback function.
Returns an array containing the results of applying the callback
function to the corresponding index of array1
(and ... if more arrays are provided)
used as arguments for the callback.
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 (as of PHP 5.3.0)
<?php
$func = function($value) {
return $value * 2;
};
print_r(array_map($func, 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($n, $m)
{
return "The number {$n} is called {$m} in Spanish";
}
function map_Spanish($n, $m)
{
return [$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
)
)
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
NULL callback with only
array1
<?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"
}
}