PHP 减去数组值 [英] PHP subtract array values

问题描述

我有一个包含键和值的数组.每个值都是一个整数.我有另一个具有相同键的数组.如何减去匹配键的所有值?也可能有些键不会出现在第二个数组中，但两个数组的长度相同.如果数组 2 中有一个不在数组 1 中的键，它的值应该保持不变.如果第一个数组中有一个不在第二个数组中的键，则应将其丢弃.我该怎么做?是否有任何内置功能?

I have an array with keys and values. Each value is an integer. I have an other array with the same keys. How can I subtract all of the values for the matching keys? Also there might be keys that do not occur in the second array but both arrays have the same length. If there is a key in array 2 that is not present in array 1 its value should be unchanged. If there is a key in the first array that is not in the second it should be thrown away. How do I do it? Is there any built-in function for this?

如果我要写一个脚本，它会是这样的 for 循环:

If I would write a script it would be some kind of for loop like this:

$arr1 = array('a' => 1, 'b' => 3, 'c' => 10);
$arr2 = array('a' => 2, 'b' => 1, 'c' => 5);
$ret = array();
foreach ($arr1 as $key => $value) {
    $ret[$key] = $arr2[$key] - $arr1[$key];
}
print_r($ret);
/*
should be: array('a' => 1, 'b' => -2, 'c' => -5)
*/

我没有在这里添加键在一个数组中而不在另一个数组中的情况.

I did not add the occasion here a key is in one array and not in the other.

推荐答案

如果您愿意，可以避免使用数组函数的 foreach.

You could avoid the foreach using array functions if you were so inclined.

提供给 array_map^docs 下面将从每个对应的 $arr2 中减去每个 $arr1 值.不幸的是，array_map 在使用多个输入数组时不会保留您的键，因此我们使用 array_combine^docs 将减去的结果合并回具有原始键的数组:

The closure provided to array_map^docs below will subtract each $arr1 value from each corresponding $arr2. Unfortunately array_map won't preserve your keys when using more than one input array, so we use array_combine^docs to merge the subtracted results back into an array with the original keys:

$arr1 = array('a' => 1, 'b' => 3, 'c' => 10);
$arr2 = array('a' => 2, 'b' => 1, 'c' => 5);

$subtracted = array_map(function ($x, $y) { return $y-$x; } , $arr1, $arr2);
$result     = array_combine(array_keys($arr1), $subtracted);

var_dump($result);

更新

与简单的 foreach 相比，我对数组函数的处理方式很感兴趣，因此我使用 Xdebug 对两者进行了基准测试.测试代码如下:

I was interested in how the array functions approach compared to a simple foreach, so I benchmarked both using Xdebug. Here's the test code:

$arr1 = array('a' => 1, 'b' => 3, 'c' => 10);
$arr2 = array('a' => 2, 'b' => 1, 'c' => 5);

function arrayFunc($arr1, $arr2) {
  $subtracted = array_map(function ($x, $y) { return $y-$x; } , $arr1, $arr2);
  $result     = array_combine(array_keys($arr1), $subtracted);
}

function foreachFunc($arr1, $arr2) {
  $ret = array();
  foreach ($arr1 as $key => $value) {
    $ret[$key] = $arr2[$key] - $arr1[$key];
  }
}

for ($i=0;$i<10000;$i++) { arrayFunc($arr1, $arr2); }
for ($i=0;$i<10000;$i++) { foreachFunc($arr1, $arr2); }

事实证明，使用 foreach 循环比使用数组函数完成相同任务快一个数量级.从下面的 KCachegrind 被调用者图片可以看出，上面代码中数组函数方法需要将近 80% 的处理时间，而 foreach 函数需要不到 5%.

As it turns out, using the foreach loop is an order of magnitude faster than accomplishing the same task using array functions. As you can see from the below KCachegrind callee image, the array function method required nearly 80% of the processing time in the above code, while the foreach function required less than 5%.

这里的教训:有时，更多语义的数组函数(令人惊讶?)在性能方面可能不如 PHP 中的老式循环.当然，您应该始终选择更具可读性/语义的选项；如果在六个月后使代码更难以理解，那么像这样的微优化是没有道理的.

The lesson here: sometimes the more semantic array functions (surprisingly?) can be inferior performance-wise to a good old fashioned loop in PHP. Of course, you should always choose the option that is more readable/semantic; micro-optimizations like this aren't justified if they make the code more difficult to understand six months down the road.

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