在 R 中，什么评估为真/假? [英] What evaluates to True/False in R?

问题描述

例如，在 Ruby 中，只有 nil 和 false 是 false.R 中的内容是什么?

For example, in Ruby, only nil and false are false. What is what in R?

例如:5==TRUE 和 5==FALSE 都评估为 FALSE.但是，1==TRUE 是 TRUE.是否有任何关于(对象、数字等)评估结果的一般规则?

e.g.: 5==TRUE and 5==FALSE both evaluate to FALSE. However, 1==TRUE is TRUE. Is there any general rule as to what (objects, numbers, etc.) evaluate to?

推荐答案

这在 ?logical 中有记录.其中的相关部分是:

This is documented on ?logical. The pertinent section of which is:

Details:

     ‘TRUE’ and ‘FALSE’ are reserved words denoting logical constants
     in the R language, whereas ‘T’ and ‘F’ are global variables whose
     initial values set to these.  All four are ‘logical(1)’ vectors.

     Logical vectors are coerced to integer vectors in contexts where a
     numerical value is required, with ‘TRUE’ being mapped to ‘1L’,
     ‘FALSE’ to ‘0L’ and ‘NA’ to ‘NA_integer_’.

那里的第二段解释了您所看到的行为，即 5 == 1L 和 5 == 0L 分别应该返回 FALSE，其中 1 == 1L 和 0 == 0L 对于 1 == TRUE 和 0 == 应该为 TRUEFALSE 分别.我相信这些不是在测试您希望他们测试的东西；比较是基于 R 中 TRUE 和 FALSE 的数值表示，即强制转换为数值时它们采用的数值.

The second paragraph there explains the behaviour you are seeing, namely 5 == 1L and 5 == 0L respectively, which should both return FALSE, where as 1 == 1L and 0 == 0L should be TRUE for 1 == TRUE and 0 == FALSE respectively. I believe these are not testing what you want them to test; the comparison is on the basis of the numerical representation of TRUE and FALSE in R, i.e. what numeric values they take when coerced to numeric.

但是，只有 TRUE 保证为 TRUE:

However, only TRUE is guaranteed to the be TRUE:

> isTRUE(TRUE)
[1] TRUE
> isTRUE(1)
[1] FALSE
> isTRUE(T)
[1] TRUE
> T <- 2
> isTRUE(T)
[1] FALSE

isTRUE 是 identical(x, TRUE) 的包装，从 ?isTRUE 我们注意到:

isTRUE is a wrapper for identical(x, TRUE), and from ?isTRUE we note:

Details:
....

     ‘isTRUE(x)’ is an abbreviation of ‘identical(TRUE, x)’, and so is
     true if and only if ‘x’ is a length-one logical vector whose only
     element is ‘TRUE’ and which has no attributes (not even names).

同样，只有 FALSE 保证完全等于 FALSE.

So by the same virtue, only FALSE is guaranteed to be exactly equal to FALSE.

> identical(F, FALSE)
[1] TRUE
> identical(0, FALSE)
[1] FALSE
> F <- "hello"
> identical(F, FALSE)
[1] FALSE

如果这与您有关，请始终使用 isTRUE() 或 identical(x, FALSE) 来检查与 TRUE 和 的等价性>FALSE 分别.== 没有按照你的想法做.

If this concerns you, always use isTRUE() or identical(x, FALSE) to check for equivalence with TRUE and FALSE respectively. == is not doing what you think it is.

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