php 从多维数组中的元素中获取最大值？
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Get the maximum value from an element in a multidimensional array?
提问by phpN00b
I'm trying to select the maximum value for a particular key in a multidimensional array. I'm having trouble "getting to" the key in question...
我正在尝试为多维数组中的特定键选择最大值。我在“找到”有问题的关键时遇到了麻烦......
So, the array (which is much more lengthy than what I'm posting here)
所以，数组（比我在这里发布的要长得多）
[0] => stdClass Object
(
[id] => 70
[cust] => 4
[dnum] => 1
[upper] => Array
(
[0] => 66
)
)
[1] => stdClass Object
(
[id] => 43
[cust] => 42
[dnum] => 2
[upper] => Array
(
[0] => 77
)
)
[2] => stdClass Object
(
[id] => 12
[cust] => 3
[dnum] => 0
[upper] => Array
(
[0] => 99
)
)
I'm trying to find the maximum "dnum" value across the entire array, so in this example, $max = 2. I know that the max function allows me to do this, but I'm not sure how to reference the dnum element without putting the whole thing in a foreach loop, and if I do that, then max wouldn't be the function to use, right?
我试图在整个数组中找到最大的“dnum”值，所以在这个例子中，$max = 2。我知道 max 函数允许我这样做，但我不确定如何引用 dnum element 没有将整个事情放在 foreach 循环中，如果我这样做，那么 max 将不是要使用的函数，对吗？
So, I can't exactly do this:
所以，我不能完全做到这一点：
$max = max($myarray[]->dnum);
Is there a way for me to do this without having to recreate the entire array?
有没有办法让我不必重新创建整个数组？
采纳答案by Tyler Carter
$max = 0;
foreach($array as $obj)
{
if($obj->dnum > $max)
{
$max = $obj->dnum;
}
}
That function would work correctly if your highest number is not negative (negatives, empty arrays, and 0s will return the max as 0).
如果您的最高数字不是负数（负数、空数组和 0 将最大值返回为 0），则该函数将正常工作。
Because you are using an object, which can have custom properties/structures, I don't believe there are really any 'predefined' functions you can use to get it. Might as well just use a foreach loop.
因为您使用的是可以具有自定义属性/结构的对象，所以我不相信您真的可以使用任何“预定义”函数来获取它。也可以只使用 foreach 循环。
You really can't get away from a foreach loop, as even internal functions use a foreach loop, it is just behind the scenes.
你真的无法摆脱 foreach 循环，因为即使是内部函数也使用 foreach 循环，它只是在幕后。
Another solution is
另一个解决方案是
$numbers = array();
foreach($array as $obj)
{
$numbers[] = $obj->dnum;
}
$max = max($numbers);
回答by cletus
In PHP 5.2 the only way to do this is to loop through the array.
在 PHP 5.2 中，唯一的方法是遍历数组。
$max = null;
foreach ($arr as $item) {
$max = $max === null ? $item->dnum : max($max, $item->dnum);
}
Note:I've seeded the result with 0 because if all the dnum values are negative then the now accepted solution will produce an incorrect result. You need to seed the max with something sensible.
注意：我将结果设为 0，因为如果所有 dnum 值都是负数，那么现在接受的解决方案将产生不正确的结果。你需要用一些明智的东西来播种最大值。
Alternatively you could use array_reduce():
或者，您可以使用array_reduce()：
$max = array_reduce($arr, 'max_dnum', -9999999);
function max_denum($v, $w) {
return max($v, $w->dnum);
}
In PHP 5.3+ you can use an anonymous function:
在 PHP 5.3+ 中，您可以使用匿名函数：
$max = array_reduce($arr, function($v, $w) {
return max($v, $w->dnum);
}, -9999999);
You can use array_map()too:
您也可以使用array_map()：
function get_dnum($a) {
return $a->dnum;
}
$max = max(array_map('get_dnum', $arr));
回答by zombat
The simplest way is probably your initial thought, which is to loop your array once, and pull out all the dnumkeys into a separate array, then call max()on that:
最简单的方法可能是您最初的想法，即循环一次数组，并将所有dnum键拉出到一个单独的数组中，然后调用max()它：
$out = array();
foreach($myarray as $obj) {
$out[] = $obj->dnum;
}
echo max($out);
You could do it without creating a separate array, but you'll end up calling max()a lot more often. Performance/memory usage will be different between the two, you could always benchmark it:
您可以在不创建单独数组的情况下执行此操作，但最终会max()更频繁地调用。两者之间的性能/内存使用情况会有所不同，您可以随时对其进行基准测试：
$first = $myarray[0]; //assume zero start index
$max = $first->dnum;
foreach($myarray as $obj) {
$max = max($max,$obj->dnum);
}
echo $max;
The only other way you could go about it would be to sort your array using usort()and a custom sorting function based on the object dnumproperties. This is probably going to be much slower than just looping your array however, so I don't think I'd recommend it unless you needed the array sorted as a side effect.
您可以进行的唯一其他方法是使用usort()基于对象dnum属性的自定义排序函数对数组进行排序。但是，这可能比仅循环数组要慢得多，所以我不认为我会推荐它，除非您需要将数组排序为副作用。
回答by DarkMukke
If you like oneliners
如果你喜欢单线
$max = max( array_map(function( $row ){ return $row->dnum; }, $myarray) );
回答by Danimal Reks
For anyone still interested, try this...
对于任何仍然感兴趣的人，试试这个......
$min = min(array_column($myarray, 'dnum'));
$max = max(array_column($myarray, 'dnum'));
