array_map()函数讲解

array_map将回调函数作用到给定数组的单元上

array array_map ( callback $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。

<?php
function cube($n)
{
return(
$n * $n * $n);
}$a = array(1, 2, 3, 4, 5);
$b = array_map(“cube”, $a);
print_r($b);
?>

这使得 $b 成为:
Array
(
[0] => 1
[1] => 8
[2] => 27
[3] => 64
[4] => 125
)
使用更多的数组的例子:
<?php
function show_Spanish($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
);
?>

上例将输出:
// 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
)

)

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。

<?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
);
?>
上例将输出:
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
)
)

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