(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)
array_map — 为数组的每个元素应用回调函数
array_map()：返回数组，是为 array 每个元素应用 callback函数之后的数组。
array_map() 返回一个 array，数组内容为 array1 的元素按索引顺序为参数调用 callback 后的结果（有更多数组时，还会传入 arrays 的元素）。
callback 函数形参的数量必须匹配 array_map() 实参中数组的数量。
callback回调函数 callable，应用到每个数组里的每个元素。
多个数组操作合并时，callback 可以设置为 null。
如果只提供了 array 一个数组，
array_map() 会返回输入的数组。
array
数组，遍历运行 callback 函数。
arrays
额外的数组列表，每个都遍历运行 callback 函数。
返回数组，包含 callback 函数处理之后 array (有多个数组时，为 arrays) 对应索引所有元素作为函数的参数。
当仅仅传入一个数组时，返回的数组会保留传入参数的键（key）。 传入多个数组时，返回的数组键是按顺序的 integer。
Example #1 array_map() 例子
<?php
function cube($n)
{
return ($n * $n * $n);
}
$a = [1, 2, 3, 4, 5];
$b = array_map('cube', $a);
print_r($b);
?>
这使得 $b 成为：
Array
(
[0] => 1
[1] => 8
[2] => 27
[3] => 64
[4] => 125
)
Example #2 array_map() 使用匿名函数 (PHP 5.3.0 起)
<?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()：使用更多的数组
<?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);
?>
以上例程会输出：
// 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
)
)
传入两个及以上的数组时，它们元素数量将会相同。因为回调函数会并行地处理相互对应的元素。 如果几个数组的元素数量不一致：空元素会扩展短那个数组，直到长度和最长的数组一样。
此函数有个有趣的用法：传入 null 作为回调函数的名称，将创建多维数组（一个数组，内部包含数组。）
Example #4 多个数组的合并操作
<?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);
?>
以上例程会输出：
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
仅有 array1 时，callback 设置为 null
<?php
$array = [1, 2, 3];
var_dump(array_map(null, $array));
?>
以上例程会输出：
array(3) {
[0]=>
int(1)
[1]=>
int(2)
[2]=>
int(3)
}
Example #6 array_map() 键（key）是 string
<?php
$arr = array("stringkey" => "value");
function cb1($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));
?>
以上例程会输出：
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"
}
}
Filling in a closure (attention: use with constants only).
<?php
$test_array = array("first_key" => "first_value",
"second_key" => "second_value");
$c = "me";
array_walk($test_array, function(&$a, $b) use ($c) { $a = "$b loves $a loves $c"; });
var_dump($test_array);
A simple one-liner to add line numbers to a text:
$i = 1; join(" \n", array_map(function($a) use(&$i) { return $i++ . ': '. $a; }, explode("\n", $text)));
Thanks to the new lambda function shorthand, you can compact the first example calculating cubic values, which is much nicer to read.
You do not have to declare a function.
$a = [1, 2, 3, 4, 5];
$b = array_map(fn($n) => $n * $n * $n, $a);
print_r($b);
ExampleArrow function php >= 7.4
Short closures, also called arrow functions, are a way of writing shorter functions in PHP. This notation is useful when passing closures to functions like array_map or array_filter
<?php
$request = [
['value'=>1],
['value'=>2],
['value'=>3],
];
print_r(
array_map(fn(array $value)=>$value['value'],$request)
);
?>
Output:
Array
(
[0] => 1
[1] => 2
[2] => 3
)
Short-hands to "array_map", fill parameter arrays:
<?php
/**
* Applies the callback to the values of the given list. Mix `array_map()` and `iterator_apply()`.
*
* @param callable $callback Callback function to run for each value in list.
* @param array $parameters Callback parameters, contain the keys "values" and "keys"(optional, auto fill).
* @return array
*/
function arr_map(?callable $callback, array $parameters): array
{
if (empty($parameters['values'])) {
throw new \InvalidArgumentException('Parameters must contain the key "values"');
}
if (! \is_iterable($parameters['values'])) {
throw new \InvalidArgumentException('Parameter "values" must be iterable');
}
if (\is_object($parameters['values'])) {
$parameters['values'] = \iterator_to_array($parameters['values']);
}
$keys = \array_keys($parameters['values']);
\array_walk(
$parameters,
function (&$value, $key) use ($keys) {
if ($key == 'keys') {
$value = $keys;
} elseif ($key != 'values') {
$value = \array_fill_keys($keys, $value);
}
}
);
return \array_map($callback, ...\array_values($parameters));
}
?>
Usage, add prefix to values:
<?php
$array = range('a', 'z');
$result = arr_map('sprintf', ['prefix_%s', 'value' => $array]));
$iterator = new ArrayIterator($array);
$result2 = arr_map('sprintf', ['prefix_%s', 'values' => $iterator]);
?>
Simple obvious thing to keep in mind:
the number of arrays passed as arguments to an array_map() function should correspond to the number of parameters defined in the callback otherwise,say if you write a function with n parameters and supply m arrays to the array_map such that m>n,array_map() ignores params at n+1 onwards. but no error or notice is issued. Of course supplying fewer arguments than declared in the function declaration throws an
ArgumentCountError
The words "is an immutable implementation" are missing...
Essentially the collection you send in can be sent to the same var you operate after map has completed, thus explicitly overwriting, but importantly the input array is not modified, so the method is (as it should be) immutable. This means if you send in `$array1` and assign result to `$array2`, you'll still have `$array1` as it was prior to the map function call.
This is entirely separate from foreach modification semantics where mostly I've seen a mix of immutable (assigning to a new object) and mutable (using key and array to update in-place `$arrayinput[$key] = doSomethingWith($value)`.
This is not a comment on the internal workings but has been tested on 5.4, 5.6, 7.0 and 7.1
If you are using Namespaces, the array_map callback expects the Fully Qualified NameSpace to be used.
For example, this won't work:
<?php
namespace Test;
function mapping_function($var) {
...
}
array_map('mapping_function', $array); //won't find 'mapping_function' here.
?>
This, however, will work:
<?php
namespace Test;
function mapping_function($var) {
...
}
array_map('Test\mapping_function', $array); //using FQNS.
?>
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.
Simplest array_map_recursive() implemention.
<?php
function array_map_recursive(callable $func, array $array) {
return filter_var($array, \FILTER_CALLBACK, ['options' => $func]);
}
?>
If you're looking for a way to get a specific set of key values (ala "pluck") you can just use array_column([['id' => 1]], 'id').
PHP 5.5.14
<?php
$columns = range(1, 100000);
$time = microtime(true);
/*
0.067003011703491 sec
24903680 byte
*/
array_map(function ($value) {
return 'p.' . $value;
}, $columns);
/*
0.042001962661743 sec
19398656 byte
*/
foreach ($columns as $key => $column) {
$columns[$key] = 'p.' . $column;
}
/*
0.05500316619873 sec
10747904 byte
*/
array_walk($columns, function (&$value, $key) {
$value = 'p.' . $value;
});
/*
0.0260009765625 sec
10747904 byte
*/
foreach ($columns as &$column) {
$column = 'p.' . $column;
}
echo microtime(true) - $time . "\n" . memory_get_peak_usage(true) . "\n";
Find an interesting thing that in array_map's callable function, late static binding does not work:
<?php
class A {
public static function foo($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)
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.
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 $arr;
}
?>
In case of you need to recursively bypass a function over the itens of an array, you can use it
<?php
function array_map_recursive($callback, $array) {
foreach ($array as $key => $value) {
if (is_array($array[$key])) {
$array[$key] = array_map_recursive($callback, $array[$key]);
}
else {
$array[$key] = call_user_func($callback, $array[$key]);
}
}
return $array;
}
?>
-----------------------------------------------------------------------
<?php
$strings = array(
'The',
array(
'quick',
'fox',
array(
'brown',
'jumps',
array(
'over',
array(
'the',
array(
'lazy',
array(
'dog'
)
)
)
)
)
)
);
print_r($strings);
$hashedString = array_map_recursive('md5', $strings);
print_r($hashedString);
?>
------------------------------------------------------------------------
Testing it, you'll obtain
<?php
/* Original array */
array (
0 => 'The',
1 =>
array (
0 => 'quick',
1 => 'fox',
2 =>
array (
0 => 'brown',
1 => 'jumps',
2 =>
array (
0 => 'over',
1 =>
array (
0 => 'the',
1 =>
array (
0 => 'lazy',
1 =>
array (
0 => 'dog',
),
),
),
),
),
),
);
/* Recursived array */
array (
0 => 'a4704fd35f0308287f2937ba3eccf5fe',
1 =>
array (
0 => '1df3746a4728276afdc24f828186f73a',
1 => '2b95d1f09b8b66c5c43622a4d9ec9a04',
2 =>
array (
0 => '6ff47afa5dc7daa42cc705a03fca8a9b',
1 => '55947829059f255e4ba2f536a2ae99fe',
2 =>
array (
0 => '3b759a9ca80234563d87672350659b2b',
1 =>
array (
0 => '8fc42c6ddf9966db3b09e84365034357',
1 =>
array (
0 => '0ffe34b4e04c2b282c5a388b1ad8aa7a',
1 =>
array (
0 => '06d80eb0c50b49a509b49f2424e8c805',
),
),
),
),
),
),
);
?>
Hope it helps you.
Cheers.
array_map becomes interesting and faster than foreach when used with existing PHP functions.
Example:
$arr1 = array(1, 2, 3, 4);
$arr2 = array(4, 3, 2, 1);
// array with min values for each key
print_r(array_map("min", $arr1, $arr2));
Result: Array ( [0] => 1 [1] => 2 [2] => 2 [3] => 1 )
// array with max values for each key
print_r(array_map("max", $arr1, $arr2));
Result: Array ( [0] => 4 [1] => 3 [2] => 3 [3] => 4 )
array_map becomes interesting and faster than foreach when used with existing PHP functions.
Example:
$arr1 = array(1, 2, 3, 4);
$arr2 = array(4, 3, 2, 1);
// array with min values for each key
print_r(array_map("min", $arr1, $arr2));
Result: Array ( [0] => 1 [1] => 2 [2] => 2 [3] => 1 )
// array with max values for each key
print_r(array_map("max", $arr1, $arr2));
Result: Array ( [0] => 4 [1] => 3 [2] => 3 [3] => 4 )
Why not an array of callbacks?
<?php
function array_maps($callbacks, $array) {
if (!$callbacks) { return $array; }
if (!is_array($callbacks) && is_string($callbacks) && function_exists($callbacks)) {
return array_map($callbacks, $array);
}
foreach($callbacks as $callback) {
if (function_exists($callback)) {
$array = array_map($callback, $array);
}
}
return $array;
}
?>
An alternative for recursive mapping;
<?php
function array_map_recursive($fn, $arr) {
$rarr = array();
foreach ($arr as $k => $v) {
$rarr[$k] = is_array($v)
? array_map_recursive($fn, $v)
: $fn($v); // or call_user_func($fn, $v)
}
return $rarr;
}
function sqr($x) {
return "$x ^ 2 = ". ($x * $x);
}
$a = array(1, 2, 3, array(4, array(5)));
$b = array_map_recursive("sqr", $a);
print_r($b);
?>
Array
(
[0] => 1 ^ 2 = 1
[1] => 2 ^ 2 = 4
[2] => 3 ^ 2 = 9
[3] => Array
(
[0] => 4 ^ 2 = 16
[1] => Array
(
[0] => 5 ^ 2 = 25
)
)
)
Hope I'm not late to the party, here's my function to apply array_map to the *keys* of an array.
Extra array arguments will be used for the callback function's parameters just like with array_map, with the difference that a string is also allowed: it will just be used to create an array of appropriate length with as each value that string. Arrays are left alone (and will be padded with nulls by array_map as needed).
<?php
//_________________________________________________
// array_map_keys($callback, $array, [$args, ..]) /
function array_map_keys($callback, $array /* [, $args ..] */) {
$args = func_get_args();
if (! is_callable($callback)) trigger_error("first argument (callback) is not a valid function", E_USER_ERROR);
if (! is_array($array)) trigger_error("second argument must be an array", E_USER_ERROR);
$args[1] = array_keys($array);
// If any additional arguments are not arrays, assume that value is wanted for every $array item.
// array_map() will pad shorter arrays with Null values
for ($i=2; $i < count($args); $i++) {
if (! is_array($args[$i])) {
$args[$i] = array_fill(0, count($array), $args[$i]);
}
}
return array_combine(call_user_func_array('array_map', $args), $array);
}
// Some examples:
$arr = array('foo'=>123, 'bar'=>456);
// simply uppercase keys:
var_dump(array_map_keys('strtoupper', $arr));
// or..
var_dump(array_map_keys(function($input) {return strtoupper($input);}, $arr));
// >> array(2) { ["FOO"]=>int(123) , ["BAR"]=> int(456) }
// Add a prefix 'myvar_':
var_dump(array_map_keys(function($input, $prefix) {return $prefix.$input;}, $arr, 'myvar_'));
// >> array(2) { ["myvar_foo"]=>int(123) , ["myvar_bar"]=>int(456) }
// Apart from the (static string) prefix, we also number them:
$arr = array('foo'=>123, 'bar'=>456, 'bazz'=>789, 'yadda'=>'0AB');
var_dump(array_map_keys(function($input, $middle, $number) {return $number.':'.$middle.$input;}, $arr, 'myvar_', range(1, count($arr))));
// >> array(4) { ["1:myvar_foo"]=>int(123) , ["2:myvar_bar"]=>int(456) , ["3:myvar_bazz"]=>int(789) , ["4:myvar_yadda"]=>string(3) "0AB" }
?>
Note that the $arr argument has to be an array, not just a Traversable/Iterator.
For instance this won't work:
<?php
$documents = $mongo->db->collection->find();
// $documents is Traversable by foreach
$ids = array_map(function($document) {
return $document['_id'];
}, $objects);
// $ids will now be NULL, because $documents wasn't an Array
?>
A solution is to first use iterator_to_array():
<?php
$ids = array_map(function($document) {
return $document['_id'];
}, iterator_to_array($objects));
// $ids will now be an array of ['_id']s
?>
But this is not very efficient: two cycles instead of one. Another solution is to use foreach: one cycle and a lot of freedom (and in the same scope).
PHP 5.3 enables us to use inline anonymous functions with array_map, cleaning up the syntax slightly.
<?php
$data = array(
array('id' => 1, 'name' => 'Bob', 'position' => 'Clerk'),
array('id' => 2, 'name' => 'Alan', 'position' => 'Manager'),
array('id' => 3, 'name' => 'James', 'position' => 'Director')
);
$names = array_map(
function($person) { return $person['name']; },
$data
);
print_r($names);
?>
This was possible (although not recommended) in prior versions of PHP 5, via create_function().
<?php
$names = array_map(
create_function('$person', 'return $person["name"];'),
$data
);
?>
You're less likely to catch errors in the latter version because the code is passed as string arguments.
These are alternatives to using a foreach:
<?php
$names = array();
foreach ($data as $row) {
$names[] = $row['name'];
}
?>
Fixed a bug with array recursion.
<?php
/**
* arrayMap function. Customized array_map function which preserves keys/associate array indexes. Note that this costs a descent amount more memory (eg. 1.5k per call)
*
* @access public
* @param callback $callback Callback function to run for each element in each array.
* @param mixed $arr1 An array to run through the callback function.
* @param array $array Variable list of array arugments to run through the callback function.
* @return array Array containing all the elements of $arr1 after applying the callback function to each one, recursively, maintain keys.
*/
function arrayMap($callback,$arr1) {
$results = array();
$args = array();
if(func_num_args()>2)
$args = (array) array_shift(array_slice(func_get_args(),2));
foreach($arr1 as $key=>$value) {
$temp = $args;
array_unshift($temp,$value);
if(is_array($value)) {
array_unshift($temp,$callback);
$results[$key] = call_user_func_array(array('self','arrayMap'),$temp);
} else {
$results[$key] = call_user_func_array($callback,$temp);
}
}
return $results;
}
?>
Another way to array_map htmlentities with a specific quote style is to create a function that does it and map that function
<?php
function map_entities( $str ) {
return htmlentities( $str, ENT_QUOTES );
}
$good_array = array_map ( 'map_entities', $bad_array );
?>
To transpose rectangular two-dimension array, use the following code:
array_unshift($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
)
)
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 $array filled with the parameter you want to give with your callback function.
I was miffed that array_map didn't have a way to pass values *and* keys to the callback, but then I realized I could do this:
function callback($k, $v) { ... }
array_map( "callback", array_keys($array), $array);
this function is really nice for recursion in php!!!
example in a class:
<?php
class test{
//private $container = array();
final public function add($key, $value){
/* recursion */
if(is_array($value)){
array_map(array($this, __FUNCTION__), array_keys($value), array_values($value));
}
/* procedural */
else{
echo $key.' => '.$value.'<br/>'.PHP_EOL;
// do stuff...
// if(!isset($this->container[$key])){
// $this->container[$key] = $value;
// }
//else{ // trigger_error() xor throw new Exception?
// echo 'allready exists!<br/>'.PHP_EOL;
//}
}
}
}
//
$array = array (
'one' => 'value1',
'two' => 'value2',
'three' => 'value3'
);
$t = new test;
$t->add($array);
?>
you could easiely do this without a class too offcourse!
used in php 5.2.5
This function behaves exactly like array_map but additionally does not reject non-array arguments. Instead, it transforms them with the array_fill function to a constant valued array of required length according to the other array arguments (if any) and executes the original array_map function.
<?php
function array_map2() {
$args = func_get_args();
$callback = array_shift($args);
$args = array_map(
create_function('$a,$max','return is_array($a)? $a: array_fill(0,$max,$a);'),
$args,array_fill(0,count($args),array_reduce($args,
create_function('$v,$w','return max($v,is_array($w)? count($w): 1);'))));
array_unshift($args,$callback);
return call_user_func_array("array_map",$args);
}
?>
Example:
<?php
$get = "first=value1&second=value2&third=value3";
print_r(array_map2("explode","=",explode("&",$get)));
?>
would print out:
<?php
Array
(
[0] => Array
(
[0] => first
[1] => value1
)
[1] => Array
(
[0] => second
[1] => value2
)
[2] => Array
(
[0] => third
[1] => value3
)
)
?>
/pmf
A note when doing something allong the lines of:
<?php
class foo {
var $var;
function bar() {
array_map(array($this, "baz"), array(1,2,3));
}
function baz($arg) {
$this->var = $this->var + $arg;
}
}
?>
This will *not* work as expected. You need to pass $this by reference as with:
array_map(array(&$this, "baz"), array(1,2,3));
or you'll be making a copy of the object each time, changing a value, then throwing the result away.