这个功能有什么问题？ - R [重复]

This question already has an answer here:

这个问题在这里已有答案：

Is floating point math broken? 24 answers
浮点数学是否破碎？ 24个答案

The function follows:

功能如下：

qual <- function(x, y, z)
{if ((abs(x - y) <= .15)&(abs(x - z) <= .15)&(abs(y - z) <= .15)){print("grade A")} 
else if((abs(x - y) <= .15)|(abs(x - z) <= .15)){print("grade B")} 
else if((abs(x - y) <= .2)|(abs(x - z) <= .2)){print("grade C")} 
else if((abs(x - y) <= .25)|(abs(x - z) <= .25)){print("grade D")} 
else {print("check manually")}}

It seems that, e.g., the output of qual(1.19, 1.04, 1.06) and qual(1.10, .95, .97)should be "grade A". However, the output is "grade A" and "grade B", respectively.

看来，例如，qual（1.19,1.04,1.06）和qual（1.10，.95，.97）的输出应该是“A级”。但是，输出分别是“A级”和“B级”。

Why is this?

为什么是这样？

1 个解决方案

#1

I think you are hitting some floating point precision problems. See Why are these numbers not equal for a full explanation.

我认为你正在遇到一些浮点精度问题。请参阅为什么这些数字不相等以获得完整的解释。

To fix this, you can use a short function that takes into account minor precision errors when comparing:

要解决此问题，您可以使用一个简短的函数，在比较时考虑较小的精度错误：

less_equal_safe <- function(x, y) {
    (x < y) | dplyr::near(x, y)
}

qual <- function(x, y, z) {
    if (less_equal_safe(abs(x - y), .15) & (abs(x - z) <= .15) &(abs(y - z) <= .15)) {
        print("grade A")
    } else if ((abs(x - y) <= .15) | (abs(x - z) <= .15)) {
        print("grade B")
    } else if ((abs(x - y) <= .2) | (abs(x - z) <= .2)) {
        print("grade C")
    } 
    else if ((abs(x - y) <= .25) | (abs(x - z) <= .25)) {
        print("grade D")
    } else {
        print("check manually")
    }
}

(note that you need the dplyr package to be installed to use dplyr::near)

（请注意，您需要安装dplyr软件包才能使用dplyr :: near）

I've only replaced the first comparison, which is the one that was causing the issue, but ideally you should replace all comparisons in your function with the float-safe function.

我只更换了第一个比较，这是造成问题的比较，但理想情况下你应该用float-safe函数替换函数中的所有比较。

#1