array_map

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

array_map — Applies 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(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, $m)
{
    return(array($n => $m));
}

$a = array(1, 2, 3, 4, 5);
$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(1, 2, 3, 4, 5);
$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
        )

)

If the array argument contains string keys then the returned array will contain string keys if and only if exactly one array is passed. If more than one argument is passed then the returned array always has 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