逻辑双重强制的基本原理是什么? [英] What is the rationale for as.logical double coercion?

问题描述

我试图理解双打的强制性理由:

I'm trying to understand the coercion rationale for doubles:

as.logical(c(-1, -0.01, 0, 0.01, 0.1,1:10))
#>  [1]  TRUE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
#> [12]  TRUE  TRUE  TRUE  TRUE

我可以看到强制发生在标量上(符号无关紧要)， FALSE仅强制为0.我为此感到惊讶， 似乎没有最接近..."或四舍五入为0L或1L的概念. 我很好奇为什么.

I can see that coercion happens on a scalar (sign doesn't matter) and that only exactly 0 is coerced to FALSE. I was surprised by this, there seems to be no notion of "closest to..." or rounding to 0L or 1L. I'm curious as to why.

我确实尝试四处寻找洞察力 此处 但没有成功.

I did try to hunt around for insight here but no success.

我还查看了此相关问题.

有人可以解释为什么我应该期望上述每个测试值 像他们一样胁迫?

Can someone explain why I should expect each of the above tested values to coerce as they do?

推荐答案

我的猜测是这是从C继承的，例如来自此处:

My guess would be that this is inherited from C, e.g. from here:

在C中，true表示为任何不等于0的数值，false表示为0

In C true is represented by any numeric value not equal to 0 and false is represented by 0

另请参见此处；目前，我找不到官方语言规范的更好来源.

Also see e.g. here; at the moment I can't find a better source for the official language specification.

Kernighan和Ritchie 2d ed的盗版副本.我在网上发现(我不希望链接到它)在p上说. 50，第3.2节"If-Else"(添加了重点):

A pirated copy of Kernighan and Ritchie 2d ed. I found online (I'd rather not link to it) says on p. 50, Section 3.2, "If-Else" (emphasis added):

对表达式求值；如果为真(，即，表达式具有非零值)，则执行语句1.如果为假(表达式为零)，并且存在其他部分，则改为执行语句2.

The expression is evaluated; if it is true (that is, if expression has a non-zero value), statement 1 is executed. If it is false (expression is zero) and if there is an else part, statement 2 is executed instead.

@hrbrmstr指出，用于转换的LOGICAL的R内部定义在Rinternals.h:

@hrbrmstr points out that the R internal definition of LOGICAL that's used for the conversion is in Rinternals.h:

#define LOGICAL(x) ((int *) DATAPTR(x))

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