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PHP Manual [array_map]

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PHP Manual || Array Functions

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

array_mapApplies the callback to the elements of the given arrays

Description

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

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().

Parameters

callback

Callback 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.

Return Values

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 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 (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 [
$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 array1

<?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"
  }
}

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
  • information about the callback type



PHP Manual || Array Functions