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array_map (PHP 4 >= 4.0.6, PHP 5) array_map --
将回调函数作用到给定数组的单元上
说明array array_map ( mixed callback, array arr1 [, array ...])
array_map() 返回一个数组，该数组包含了
arr1 中的所有单元经过
callback 作用过之后的单元。callback
接受的参数数目应该和传递给
array_map() 函数的数组数目一致。
例子 1. array_map() 例子 |
<?php
function cube($n) {
return $n*$n*$n;
}
$a = array(1, 2, 3, 4, 5);
$b = array_map("cube", $a);
print_r($b);
?>
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这使得 $b 成为：
Array
(
[0] => 1
[1] => 8
[2] => 27
[3] => 64
[4] => 125
) |
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例子 2. array_map() - 使用更多的数组 |
<?php
function show_Spanish($n, $m) {
return "The number $n is called $m in Spanish";
}
function map_Spanish($n, $m) {
return array ($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);
?>
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结果为：
// 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
)
) |
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通常使用了两个或更多数组时，它们的长度应该相同，因为回调函数是平行作用于相应的单元上的。如果数组的长度不同，则最短的一个将被用空的单元扩充。
本函数一个有趣的用法是构造一个数组的数组，这可以很容易的通过用 NULL 作为回调函数名来实现。
例子 3. 建立一个数组的数组 |
<?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);
?>
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以上程序输出为：
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
)
) |
参见 array_filter()，array_reduce()
和 array_walk()。
bishop
27-Mar-2002 07:33
Sometimes you might be interested in performing a "deep" map,
where you apply the callback to all elements in the array, even if the
elements are stuck deep inside of some array(array(array(...)))
business.
Here's an example PHP4 function that handles this case,
with a little bit more flexible (and potentially more error-prone) callback
parameter:
<?php
function deepmap($cb, $x) {
if (is_array($x)) {
$it = array();
foreach ($x as
$k => $v) {
$it["$k"] = deepmap($cb,
$x["$k"]);
}
return $it;
} else
{
$cmd = "return (" .
str_replace('$__', $x, $cb) .
");";
return eval($cmd);
}
}
So, you could do, for
example:
$some_odds = array(1, 3, 5);
$some_evens = array(0,
2, 4, 6);
$some_nums = array($some_odds,
array($some_evens));
deepmap('pow($__, 2)',
$some_odds);
deepmap('pow($__, 2)',
$some_nums);
?>
Both examples square each element of the
arrays, making sure to keep the array structure intact.
Note that
the callback function needs to be a) quoted, and b) include the special
string $__ (dollar double underscore); deepmap replaces $__ in the function
call with whatever the current element is.
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array_keys
