什么计算为真/假R中？ [英] What evaluates to True/False in R?

问题描述

例如，在Ruby中，只有零和虚假的都是假的。 R中的是什么？

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

例如： 5 == TRUE 和 5 == FALSE 这两个评估为FALSE。然而， 1 == TRUE 是 TRUE 。是否有任何一般规则，以什么（对象，数字等），计算结果为？

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

这是在案？逻辑。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_’.

第二段有解释你所看到，该行为即 5 == 1L 和 5 == 0L 分别为，这应该都返回 FALSE ，其中以 1 == 1L 和 0 == 0L 应为TRUE 1 == TRUE 和 0 == FALSE 分别。我相信这些不是测试你希望他们考什么;比较结果为 TRUE的数值再presentation 和 FALSE 在R，即什么数字的基础上，当强制转换为数字，他们采取的值。

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.

然而，只有 TRUE 被保证的是 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运算是相同的包装（X，TRUE），并从？ IsTrue运算我们注意到：

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).

因此​​，通过相同的美德，只有 FALSE 是保证正好等于 FALSE 。

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

如果这涉及到你，总是用 IsTrue运算（）或相同（X，FALSE）检查等价与 TRUE 和 FALSE 分别。 == 是不是做你认为它是。

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.

这篇关于什么计算为真/假R中？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！