通过无循环键多维数组的和值 [英] Sum values of multidimensional array by key without loop

问题描述

我有这样的：

Array ( [0] => Array ( [f_count] => 1 [uid] => 105 ) 
[1] => Array ( [f_count] => 0 [uid] => 106 ) 
[2] => Array ( [f_count] => 2 [uid] => 107 ) 
[3] => Array ( [f_count] => 0 [uid] => 108 ) 
[4] => Array ( [f_count] => 1 [uid] => 109 ) 
[5] => Array ( [f_count] => 0 [uid] => 110 ) 
[6] => Array ( [f_count] => 3 [uid] => 111 ) )  

我需要的是：7，这是f_count列的总和。
我一直在试图找出这一点的一对夫妇小时。我以为array_sum会的工作，但不能与一个多维数组。于是，我试着找出如何通过取消设置（）或剪接或任何其他的f_counts隔离，但是每一个解决方案似乎涉及一个foreach循环。我搞砸与array_map，array_walk，并没有用其他人。我还没有发现用多维数组行之有效的功能。

What I need is: "7", which is the the sum of the f_count column. I've been trying to figure this out for a couple hours. I thought array_sum would work, but not with a multidimensional array. So, I've tried figuring out how to isolate the f_counts by unset()or splicing or anything else, but every solution seems to involve a foreach loop. I've messed with array_map, array_walk, and others to no avail. I haven't found a function that works well with multidimensional arrays.

我运行PHP 5.4。

I'm running PHP 5.4.

可有人请告诉我如何总结这列没有一个foreach循环？

Can someone please show me how to sum that column without a foreach loop?

如果有帮助，对f_count值永远不会高于100，和UID值将始终大于100。

If it helps, the f_count values will never be higher than 100, and the uid values will always be greater than 100.

另外，如果有一种方式来运行我的查询不同使得阵列是不是多维的，这显然会正常工作。

Alternatively, if there's a way to run my query differently such that the array is not multidimensional, that would obviously work as well.

$query = "SELECT f_count, uid FROM users WHERE gid=:gid";
...
$array = $stmt->fetchAll();

我使用的PDO。

I'm using PDO.

推荐答案

您需要夫妇它 array_map（） 首先选择 f_count 列：

array_sum(array_map(function($item) { 
    return $item['f_count']; 
}, $arr));

当然，在内部，这个执行双循环;它只是你没有看到它的code内。你可以使用 array_reduce（） 摆脱一个循环的：

Of course, internally, this performs a double loop; it's just that you don't see it inside the code. You could use array_reduce() to get rid of one loop:

array_reduce($arr, function(&$res, $item) {
    return $res + $item['f_count'];
}, 0);

不过，如果速度是唯一感兴趣的，的foreach 仍然是最快的：

$sum = 0;
foreach ($arr as $item) {
    $sum += $item['f_count'];
}

这是多亏了这些变量的局部性您使用的，即有用于计算最后一笔没有函数调用。

This is thanks to the "locality" of the variables that you're using, i.e. there are no function calls used to calculate the final sum.

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