问题描述
我正在尝试比较 R 中的两个数字作为 if 语句条件的一部分:
I'm trying to compare two numbers in R as a part of a if-statement condition:
(a-b) >= 0.5
在这个特定的例子中，a = 0.58 和 b = 0.08...但 (a-b) >= 0.5 是假的.我知道使用 == 进行精确数字比较的危险，这似乎是相关的:
In this particular instance, a = 0.58 and b = 0.08... and yet (a-b) >= 0.5 is false. I'm aware of the dangers of using == for exact number comparisons, and this seems related:
(a - b) == 0.5) 是假的，而
all.equal((a - b), 0.5) 为真.
我能想到的唯一解决方案是有两个条件:(a-b) >0.5 |all.equal((a-b), 0.5).这有效，但这真的是唯一的解决方案吗?我应该永远发誓不使用 = 系列比较运算符吗?
The only solution I can think of is to have two conditions: (a-b) > 0.5 | all.equal((a-b), 0.5). This works, but is that really the only solution? Should I just swear off of the = family of comparison operators forever?
为清楚起见进行我知道这是一个浮点问题.更根本的是，我要问的是:我该怎么办?在 R 中处理大于或等于比较的明智方法是什么，因为 >= 真的不能被信任?
Edit for clarity: I know that this is a floating point problem. More fundamentally, what I'm asking is: what should I do about it? What's a sensible way to deal with greater-than-or-equal-to comparisons in R, since the >= can't really be trusted?
推荐答案
我从不喜欢 all.equal 来处理这些事情.在我看来，宽容有时会以神秘的方式发挥作用.为什么不检查大于小于 0.05 的容差
I've never been a fan of all.equal for such things. It seems to me the tolerance works in mysterious ways sometimes. Why not just check for something greater than a tolerance less than 0.05
tol = 1e-5
(a-b) >= (0.05-tol)
总的来说，没有四舍五入，只使用传统逻辑，我发现直接逻辑比 all.equal 更好
In general, without rounding and with just conventional logic I find straight logic better than all.equal
如果x == y 那么x-y == 0.也许 x-y 不完全是 0 所以对于这种情况我使用
If x == y then x-y == 0. Perhaps x-y is not exactly 0 so for such cases I use
abs(x-y) <= tol
无论如何你都必须为 all.equal 设置容差，这比 all.equal 更紧凑和直接.
You have to set tolerance anyway for all.equal and this is more compact and straightforward than all.equal.
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