php 开发经常遇到数组处理，会涉及到题目中这几个函数。这个函数功能类似，很多时候容易混淆。
array_walk：array_walk — 使用用户自定义函数对数组中的每个元素做回调处理
1. 用户自定义的函数处理每一个元素
2. 直接修改原数组，不会创建新的数组
3. 可以传递额外的参数
Example #1 :
<?php $fruits = array("d" => "lemon", "a" => "orange", "b" => "banana", "c" => "apple"); function test_alter(&$item1, $key, $prefix) { $item1 = "$prefix: $item1"; } function test_print($item2, $key) { echo "$key. $item2<br />\n"; } echo "Before ...:\n"; array_walk($fruits, 'test_print'); array_walk($fruits, 'test_alter', 'fruit'); echo "... and after:\n"; array_walk($fruits, 'test_print'); ?>
//运行结果Before ...:
d. lemon
a. orange
b. banana
c. apple ... and after:
d. fruit: lemon
a. fruit: orange
b. fruit: banana
c. fruit: apple array_map
array_map — 为数组的每个元素应用回调函数
1. 回调函数，应用到每个数组里的每个元素
2. 可以处理多个数组，合并处理
3. 返回新建的数组
4. 传入 NULL 作为回调函数的名称，将创建多维数组
5. 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。
Example #1：
<?php
function cube($n)
{
return($n * $n * $n);
}
$a = array(1, 2, 3, 4, 5);
$b = array_map("cube", $a);
print_r($b);
?>
//运行结果
Array
(
[0] => 1
[1] => 8
[2] => 27
[3] => 64
[4] => 125
)
Example #2：
<?php
$func = function($value) {
return $value * 2;
};
print_r(array_map($func, range(1, 5)));
?>
//运行结果
Array
(
[0] => 2
[1] => 4
[2] => 6
[3] => 8
[4] => 10
)
Example #3：
<?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);
?>
//运行结果
// 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 $d
Array
(
[0] => Array
(
[1] => uno
)
[1] => Array
(
[2] => dos
)
[2] => Array
(
[3] => tres
)
[3] => Array
(
[4] => cuatro
)
[4] => Array
(
[5] => cinco
)
* array_filter — 用回调函数过滤数组中的单元*
1. 依次将 array 数组中的每个值传递到 callback 函数。如果 callback 函数返回 true，则 array 数组的当前值会被包含在返回的结果数组中。数组的键名保留不变。
2. 如果没有提供 callback 函数， 将删除 array 中所有等值为 FALSE 的条目。
3. ARRAY_FILTER_USE_KEY - callback接受键名作为的唯一参数，ARRAY_FILTER_USE_BOTH - callback同时接受键名和键值
Example 1:
<?php
function odd($var)
{
// returns whether the input integer is odd
return($var & 1);
}
function even($var)
{
// returns whether the input integer is even
return(!($var & 1));
}
$array1 = array("a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5);
$array2 = array(6, 7, 8, 9, 10, 11, 12);
echo "Odd :\n";
print_r(array_filter($array1, "odd"));
echo "Even:\n";
print_r(array_filter($array2, "even"));
?>
//运行结果
Odd :
Array
(
[a] => 1
[c] => 3
[e] => 5
)
Even:
Array
(
[0] => 6
[2] => 8
[4] => 10
[6] => 12
Example #2:
<?php $entry = array( 0 => 'foo', 1 => false, 2 => -1, 3 => null, 4 => '' ); print_r(array_filter($entry)); ?>
//运行结果
Array
(
[0] => foo
[2] => -1
)
Example #3：