php 如何获得一个数字的符号？

How to get sign of a number?

提问by hakre

Is there a (simple) way to get the "sign" of a number (integer) in PHP comparable to gmp_sign^Docs:

是否有一种（简单的）方法可以在 PHP 中获取与gmp_sign^Docs相当的数字（整数）的“符号” ：

• -1 negative
• 0 zero
• 1 positive

• -1 负
• 0 零
• 1 阳性

I remember there is some sort of compare function that can do this but I'm not able to find it at the moment.

我记得有某种比较功能可以做到这一点，但我目前无法找到它。

I quickly compiled this (Demo) which does the job, but maybe there is something more nifty (like a single function call?), I would like to map the result onto an array:

我很快编译了这个（Demo）来完成这项工作，但也许还有更漂亮的东西（比如单个函数调用？），我想将结果映射到一个数组上：

$numbers = array(-100, 0, 100);

foreach($numbers as $number)
{
   echo $number, ': ', $number ? abs($number) / $number : 0, "\n";
}

(this code might run into floating point precision problems probably)

（此代码可能会遇到浮点精度问题）

Related: Request #19621 Math needs a "sign()" function

相关：请求#19621 Math 需要一个“sign()”函数

回答by Milosz

Here's a cool one-liner that will do it for you efficiently and reliably:

这是一个很酷的单线，可以高效可靠地为您完成：

function sign($n) {
    return ($n > 0) - ($n < 0);
}

回答by kdojeteri

In PHP 7 you should use the combined comparison operator(<=>):

在 PHP 7 中，您应该使用组合比较运算符( <=>)：

$sign = $i <=> 0;

回答by hakre

A variant to the above in my question I tested and which works as well and has not the floating point problem:

在我测试的问题中，上述问题的一个变体也可以正常工作并且没有浮点问题：

min(1, max(-1, $number))

---

---

Edit:The code above has a flaw for float numbers (question was about integer numbers) in the range greater than -1and smaller than 1which can be fixed with the following shorty:

编辑：上面的代码对于大于-1和小于范围内的浮点数（问题是关于整数）有一个缺陷1，可以用以下短文修复：

min(1, max(-1, $number == 0 ? 0 : $number * INF))

That one still has a flaw for the float NANmaking it return -1always. That might not be correct. Instead one might want to return 0as well:

那个仍然有一个浮动的缺陷，NAN使它-1总是返回。那可能不正确。相反，人们可能也想返回0：

min(1, max(-1, (is_nan($number) or $number == 0) ? 0 : $number * INF))

回答by rocksportrocker

You can nest ternary operators:

您可以嵌套三元运算符：

echo $number, ': ',  ($number >= 0 ? ($number == 0 ? 0 : 1) : -1 )

This has no problem with floating point precision and avoids an floating point division.

这对浮点精度没有问题，并避免了浮点除法。

回答by zzzzBov

What's wrong with this form?

这个表格有什么问题？

if ( $num < 0 )
{
  //negative
}
else if ( $num == 0 )
{
  //zero
}
else
{
  //positive
}

or ternary:

或三元：

$sign = $num < 0 ? -1 : ( $num > 0 ? 1 : 0 );

Not sure of the performance of absvs value comparison, but you could use:

不确定absvs 值比较的性能，但您可以使用：

$sign = $num ? $num / abs($num) : 0;

and you could turn any of them into a function:

你可以把它们中的任何一个变成一个函数：

function valueSign($num)
{
  return $sign = $num < 0 ? -1 : ( $num > 0 ? 1 : 0 );
  //or
  return $sign = $num ? $num / abs($num) : 0;
}

---

---

I suppose you could be talking about gmp_cmp, which you could call as gmp_cmp( $num, 0 );

我想你可能在谈论gmp_cmp，你可以称之为gmp_cmp( $num, 0 );

回答by Rolf

I think that gmp_sign is not very efficient because it expects a GMP or string. ($n ? abs($n)/$n : 0) is mathematically correct, but the division costs time. The min/max solutions seem to get unnecessary complex for floats.

我认为 gmp_sign 不是很有效，因为它需要一个 GMP 或字符串。($n ? abs($n)/$n : 0) 在数学上是正确的，但除法需要时间。最小/最大解决方案似乎对浮动变得不必要的复杂。

($n > 0) - ($n < 0) always does 2 tests and one subtraction ($n < 0 ? -1 : ($n > 0 ? 1 : 0) does one or two tests and no arithmetic, it should be most efficient. But I don't believe that the difference will be relevant for most use cases.

($n > 0) - ($n < 0) 总是做 2 个测试和一个减法 ($n < 0 ? -1 : ($n > 0 ? 1 : 0) 做一两个测试而不是算术，它应该是最有效的。但我认为这种差异与大多数用例无关。

回答by sansig

I know this is late but what about simply dividing the number by the abs() of itself?

我知道这已经晚了，但是简单地将数字除以自身的 abs() 怎么样？

Something like:

就像是：

function sign($n) {
    return $n/(abs($n));
}

Put whatever error handling you want for div by zero.

将 div 所需的任何错误处理归零。

回答by Toto

Use strcmp^Docs:

使用strcmp^文档：

echo $number, ': ', strcmp($number, 0), "\n";

回答by Yeroon

Here's one without loop:

这是一个没有循环的：

function sign($number){
    echo $number, ': ', $number ? abs($number) / $number : 0, "\n";
}

$numbers = array(-100, 0, 100);

array_walk($numbers, 'sign');