PHP：我可以在 array_map 函数中获取索引吗？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/5868457/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
PHP: Can I get the index in an array_map function?
提问by Ollie Glass
I'm using a map in php like so:
我在 php 中使用地图，如下所示：
function func($v) {
return $v * 2;
}
$values = array(4, 6, 3);
$mapped = array_map(func, $values);
var_dump($mapped);
Is it possible to get the index of the value in the function?
是否可以获取函数中值的索引？
Also - if I'm writing code that needs the index, should I be using a for loop instead of a map?
另外 - 如果我正在编写需要索引的代码，我应该使用 for 循环而不是地图吗？
回答by Aron Rotteveel
Sure you can, with the help of array_keys():
当然可以，在帮助下 array_keys():
function func($v, $k) {
// key is now $k
return $v * 2;
}
$values = array(4, 6, 3);
$mapped = array_map(func, $values, array_keys($values));
var_dump($mapped);
回答by Warbo
When mapping an anonymous function over an anonymous array, there is no way to access the keys:
在匿名数组上映射匿名函数时，无法访问键：
array_map(
function($val) use ($foo) { /* ... */ },
array(key1 => val1,
key2 => val2,
/* ... */));
array_reduce doesn't get access to the keys either. array_walk can access keys, but the array is passed by reference, which requires a layer of indirection.
array_reduce 也无法访问密钥。array_walk 可以访问键，但是数组是通过引用传递的，需要一层间接。
Some solutions are:
一些解决方案是：
Array of pairs
对数组
This is bad, since we're changing the original array. Plus the boilerplate "array()" calls increase linearly with the length of the array:
这很糟糕，因为我们正在更改原始数组。加上样板“array()”调用随着数组的长度线性增加：
array_map(
function($pair) use ($foo) {
list($key, $val) = $pair;
/* ... */
},
array(array(key1, val1),
array(key2, val2),
/* ... */));
Temporary variable
临时变量
We're acting on the original array, and the boilerplate is constant, but we can easily clobber an existing variable:
我们对原始数组进行操作，样板文件是常量，但我们可以轻松破坏现有变量：
$i_hope_this_does_not_conflict = array(key1 => val1,
key2 => val2,
/* ... */);
array_map(
function($key, $val) use ($foo) { /* ... */ },
array_keys($i_hope_this_does_not_conflict),
$i_hope_this_does_not_conflict);
unset($i_hope_this_does_not_conflict);
One-shot function
一键功能
We can use function scope to prevent clobbering existing names, but have to add an extra layer of "use":
我们可以使用函数作用域来防止破坏现有名称，但必须添加一个额外的“使用”层：
call_user_func(
function($arr) use ($foo) {
return array_map(function($key, $val) use ($foo) { /* ... */ },
array_keys($arr),
$arr);
},
array(key1 => val1,
key2 => val2,
/* ... */));
Multi-argument one-shot function
多参数一次性功能
We define the function we're mapping in the original scope to prevent the "use" boilerplate):
我们定义了我们在原始范围内映射的函数以防止“使用”样板）：
call_user_func(
function($f, $arr) {
return array_map($f, array_keys($arr), $arr);
},
function($key, $val) use ($foo) { /* ... */ },
array(key1 => val1,
key2 => val2,
/* ... */));
New function
新功能
The interesting thing to note is that our last one-shot function has a nice, generic signature and looks a lot like array_map. We might want to give this a name and re-use it:
有趣的是，我们的最后一个一次性函数有一个很好的通用签名，看起来很像 array_map。我们可能想给它一个名字并重新使用它：
function array_mapk($f, $arr) {
return array_map($f, array_keys($arr), $arr);
}
Our application code then becomes:
然后我们的应用程序代码变为：
array_mapk(
function($key, $val) use ($foo) { /* ... */ },
array(key1 => val1,
key2 => val2,
/* ... */));
Indirect Array Walk
间接数组遍历
When writing the above I'd ignored array_walk since it requires its argument to be passed by reference; however, I've since realised that it's easy to work around this using call_user_func. I think this is the best version so far:
在编写上述内容时，我忽略了 array_walk，因为它需要通过引用传递其参数；然而，我后来意识到使用 call_user_func 很容易解决这个问题。我认为这是迄今为止最好的版本：
call_user_func(
'array_walk',
array(key1 => val1,
key2 => val2,
/* ... */),
function($val, $key) use ($foo) { /* ... */ });
回答by Fábio Zangirolami
Very simple:
很简单：
Only array_map fuction: does not have index key!
只有 array_map 功能：没有索引键！
$params = [4,6,2,11,20];
$data = array_map(function($v) { return ":id{$v}";}, $params);
array (size=5)
0 => string ':id4' (length=4)
1 => string ':id6' (length=4)
2 => string ':id2' (length=4)
3 => string ':id11' (length=5)
4 => string ':id20' (length=5)
Now, combine with array_keys:
现在，结合 array_keys：
$data = array_map(
function($k) use ($params) { return ":id{$k}_${params[$k]}"; },
array_keys($params)
);
array (size=5)
0 => string ':id0_4' (length=6)
1 => string ':id1_6' (length=6)
2 => string ':id2_2' (length=6)
3 => string ':id3_11' (length=7)
4 => string ':id4_20' (length=7)
