检查空数组:计数与空数组
这个问题关于'如何判断 PHP array isempty' 让我想到了这个问题
在确定数组是否为空时,是否有理由使用 count
而不是 empty
?
我个人的想法是,如果 2 对于空数组的情况是等效的,您应该使用 empty
因为它为布尔问题提供了布尔答案。从上面链接的问题来看,似乎 count($var) == 0
是流行的方法。对我来说,虽然技术上是正确的,但毫无意义。例如问:$var,你是空的吗?答:7。嗯...
我是否应该使用 count == 0
来代替,或者只是个人品味问题?
正如其他人在现已删除的答案的评论中指出的那样, count
将对大型数组产生性能影响,因为它必须计算所有元素,而 empty
可以立即停止因为它知道它不是空的。因此,如果在这种情况下它们给出相同的结果,但 count
可能效率低下,那么我们为什么要使用 count($var) == 0
呢?
This question on 'How to tell if a PHP array is empty' had me thinking of this question
Is there a reason that count
should be used instead of empty
when determining if an array is empty or not?
My personal thought would be if the 2 are equivalent for the case of empty arrays you should use empty
because it gives a boolean answer to a boolean question. From the question linked above, it seems that count($var) == 0
is the popular method. To me, while technically correct, makes no sense. E.g. Q: $var, are you empty? A: 7. Hmmm...
Is there a reason I should use count == 0
instead or just a matter of personal taste?
As pointed out by others in comments for a now deleted answer, count
will have performance impacts for large arrays because it will have to count all elements, whereas empty
can stop as soon as it knows it isn't empty. So, if they give the same results in this case, but count
is potentially inefficient, why would we ever use count($var) == 0
?
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我通常使用
空
。我不确定为什么人们会真正使用 count - 如果数组很大,那么 count 需要更长的时间/有更多的开销。如果您只是需要知道数组是否为空,则使用empty。I generally use
empty
. Im not sure why people would use count really - If the array is large then count takes longer/has more overhead. If you simply need to know whether or not the array is empty then use empty.我很好奇哪一个实际上更快,因此我制作了一个简单的脚本来对这些函数进行基准测试。
由于我正在这样做,所以我还尝试检查通常与 count()/empty() 相关的操作的性能
使用 PHP 5.4.39:
使用 HipHop VM 3.6.1 (dbg)
结论,如果您是使用 PHP:
empty() 在这两种情况下都比 count() 快得多,使用空数组和填充数组
count() 对满数组或空数组执行相同的操作。
进行简单的 IF 或仅进行布尔运算是相同的。
IF/ELSE 的效率比 (?:) 稍高。除非您使用中间的表达式进行数十亿次迭代,否则它完全无关紧要。
如果您使用 HHVM,结论是:
empty() 比 count() 快一点点,但并不明显。
[其余部分与 PHP 中的相同]
总而言之,如果您只需要知道数组是否为空,请始终使用empty();
这只是一个奇怪的测试,只是在没有考虑很多事情的情况下完成的。它只是一个概念证明,可能无法反映生产中的操作。
I was curious to see which one was actually faster so I made a simple script to benchmark those functions.
Since I was doing it I also tried to check the performance doing operations that would normally be associated with count()/empty()
Using PHP 5.4.39:
Using HipHop VM 3.6.1 (dbg)
Conclusions if you're using PHP:
empty() is much much faster than count() in both scenarios, with an empty and populated array
count() performs the same with a full or empty array.
Doing a simple IF or just a Boolean operation is the same.
IF/ELSE is very slightly more efficient than ( ? : ). Unless you're doing billions of iterations with expressions in the middle it is completely insignificant.
Conclusions if you're using HHVM:
empty() is a teeny-weeny bit faster than count() but insignificantly so.
[ The rest is the same as in PHP ]
In conclusion of the conclusion, if you just need to know if the array is empty always use empty();
This was just a curious test simply done without taking many things into account. It is just a proof of concept and might not reflect operations in production.
我认为这只是个人喜好。有些人可能会说
empty
更快(例如 http://jamessocol.com/projects /count_vs_empty.php),而其他人可能会说count
更好,因为它最初是为数组创建的。empty
更通用,可以应用于其他类型。php.net 对于
count
给出以下警告:换句话说,如果未设置该变量,您将收到 PHP 的通知,指出该变量未定义。因此,在使用
count
之前,最好使用isset
检查变量。对于empty
来说,这不是必需的。I think it's only personal preference. Some people might say
empty
is faster (e.g. http://jamessocol.com/projects/count_vs_empty.php) while others might saycount
is better since it was originally made for arrays.empty
is more general and can be applied to other types.php.net gives the following warning for
count
though :In other words, if the variable is not set, you will get a notice from PHP saying it's undefined. Therefore, before using
count
, it would be preferable to check the variable withisset
. This is not necessary withempty
.有,当您需要在知道其大小的非空数组上执行某些操作时:
但我不建议使用 count ,除非您 100% 确定您正在计算的是一个数组。最近我一直在调试代码,其中错误函数返回
FALSE
而不是空数组,我发现的是:输出:
所以从那时起我使用
empty
或 < code>if(array() === $array) 以确保我的 array 是空的。There is, when you need to do something on non-empty array knowing it's size:
But I wouldn't recommend using count, unless you are 100% sure, that what you are counting is an array. Lately I have been debugging code, where on error function was returning
FALSE
instead of empty array, and what I discovered was:output:
So since then I am using
empty
orif(array() === $array)
to be sure that I have array that is empty.count()
似乎与实现ArrayAccess/Countable
的类数组接口配合得更好。对于这些类型的对象,即使它们没有元素,empty()
也会返回 false。通常,这些类将实现 Countable 接口,因此如果问题是“此集合是否包含元素?”如果不对实现做出假设,那么count()
是一个更好的选择。count()
seems to work better with array-like interfaces that implementArrayAccess/Countable
.empty()
returns false for these kinds of objects even if they have no elements. Typically these classes will implement theCountable
interface, so if the question is "Does this collection contain elements?" without making an assumption about the implementation, thencount()
is a better option.或者,您可以将变量转换为布尔值(隐式或显式):
如果未定义变量,此方法会生成
E_NOTICE
,类似于count()
。有关详细信息,请参阅有关类型比较的 PHP 手册页面。
Alternatively, you can cast the variable as a boolean (implicitly or explicitly):
This method does generate an
E_NOTICE
if the variable is not defined, similarly tocount()
.For more information, see the PHP Manual page on type comparisons.
没有充分的理由选择
count($myArray) == 0
而不是empty($myArray)
。它们具有相同的语义。有些人可能会发现其中一个比另一个更具可读性。其中一个的性能可能比另一个稍好一些,但它不太可能成为绝大多数 php 应用程序中的重要因素。出于所有实际目的,选择取决于品味。There is no strong reason to prefer
count($myArray) == 0
overempty($myArray)
. They have identical semantics. Some might find one more readable than the other. One might perform marginally better than the other but it's not likely to be a significant factor in the vast majority of php applications. For all practical purposes, the choice is a matter of taste.我个人更喜欢编码优雅(与我的具体用例相关)。我同意 Dan McG 的观点,因为 count() 没有以正确的数据类型(在本例中为布尔值)响应相关测试,迫使开发人员编写更多代码来填充“if”语句。
这是否对性能有任何重大影响只有对于非常大的数组才有争议(在大多数设置中你可能不会有足够的内存分配)。
特别是当涉及到 PHP 的 $_POST 数组时,我认为编写/查看似乎更“合乎逻辑”:
My personal preference is more for coding elegance (in relation to my specific use-case). I agree with Dan McG inasmuch that count() isn't responding with the correct datatype (in this case boolean) for the test in question forcing the developer to write more code to fill an 'if' statement.
Whether this has any significant impact on performance is only debatable for extremely large arrays (which you probably won't have enough memory allocation for anyway in most setups).
Particularly when it comes to PHP's $_POST array, it seems much more "logical" in my opinion to write/see:
希望这可以帮助某人,即使它已经得到回答(并争论了一些什么)。在我自己的场景中,我知道我的所有数组都有 7 个元素(在我的代码中之前进行了检查),并且我正在执行一个
array_diff
,它当然会在相等时返回一个为零的数组。我有 34 秒的时间来计数,17 秒的时间为空。两者都给了我相同的计算,所以我的代码仍然没问题。
但是,您也可以尝试
==
或===
,如 PHP - 检查两个数组是否相等。我想说的最好的方法是尝试count
与empty
与== 空数组
,然后看看哪个能提供您自己的最佳性能。就我而言,count
是最慢的,所以我现在使用empty
...接下来将检查serialize
Hope this might help someone even though it has already been answered (and debated some what). In my own scenario, I know all my arrays all have 7 elements (checks were made earlier in my code) and I am performing an
array_diff
which of course returns an array of zero when equal.I had 34 sec for
count
and 17 sec forempty
. Both give me the same calculations so my code is still fine.However you can also try the
==
or===
as in PHP - Check if two arrays are equal. The best I would say is trycount
vsempty
vs== empty array
, then see which gives your own best perfs. In my casecount
was the slowest so I am usingempty
now... will be checkingserialize
next有时使用空是必须的。例如此代码:
如果您像这样运行此代码: http://phpfiddle.org/main /code/g9x-uwi
你会得到这样的输出:
因此,如果你
计算
空的 glob 输出,你会得到错误的输出。您应该检查是否为空。来自 glob 文档:
另请检查这个问题:
为什么 count(false) 返回 1?
Sometimes using empty is a must. For example this code:
If you run this code like this: http://phpfiddle.org/main/code/g9x-uwi
You get this output:
So if you
count
the empty glob output you get wrong output. You should check for emptiness.From glob documentation:
Also check this question:
Why count(false) return 1?
由于解析为负数的变量将返回
int(1)
和count()
我更喜欢
($array === [] || !$array)< /code> 测试空数组。
是的,我们应该期望一个空数组,但是我们不应该期望在没有强制返回类型的情况下函数能够得到良好的实现。
count() 的示例
Since a variable parsed as negative would return
int(1)
withcount()
I prefer
($array === [] || !$array)
to test for an empty array.Yes, we should expect an empty array, but we shouldn't expect a good implementation on functions without enforced return types.
Examples with
count()
我改变了主意,谢谢。
好的,
empty
和count
的用法没有区别。从技术上讲,count
应该用于数组,empty
可以用于数组和字符串。因此,在大多数情况下,它们是可以互换的,如果您查看 php 文档,如果您处于empty
状态,您将看到count
的建议列表,反之亦然。I remade my mind guys, thanks.
Ok, there is no difference between the usage of
empty
andcount
. Technically,count
should be used for arrays, andempty
could be used for arrays as well as strings. So in most cases, they are interchangeable and if you see the php docs, you will see the suggestion list ofcount
if you are atempty
and vice versa.