问题描述
我不是要解决任何特定问题，而是要尝试学习 R 并理解其逻辑否定运算符！"记录在页面 http://stat.ethz.ch/R-manual/R-devel/library/base/html/Logic.html
I am not trying to solve any particular problem, but trying to learn R and understand its logical negation operator "!" documented on page http://stat.ethz.ch/R-manual/R-devel/library/base/html/Logic.html
它在与 = 组合使用时对我有用，例如:
It works for me when used in combination with =, in expressions such as:
1 != 2
TRUE
但我不能完全理解这个运算符的独立应用.例如，我可以使用它来选择列表中没有特定名称的元素吗?这是我尝试这样做，但没有奏效:
But I can't quite comprehend standalone application of this operator. For instance, can I use it to select elements of the list which do not have specific name. Here's my attempt to do that, but it did not work:
vector1 <- 1:5 # just making vector of 5 numbers
vector2 <- 5:1 # same vector backwards
list <- list(Forward=vector1, Backwards=vector2) # producing list with two elements
x = "Forward"
list[!x]
我的输出是:
Error in !x : invalid argument type
在这种情况下我的逻辑出错的任何提示，以及除了 != case 之外该运算符还有哪些其他好的用途，我们将不胜感激.
Will appreciate any hints on where my logic goes wrong in this case, and what are other good uses of this operator except for != case.
谢谢！谢尔盖
推荐答案
首先，最好不要将 != 视为 ! 作用于 =，而是作为一个单独的二元运算符.
First, it's probably best not to think of != as ! acting on =, but rather as a separate binary operator altogether.
一般来说，! 应该只应用于布尔向量.所以这可能更像你所追求的:
In general, ! should only be applied to boolean vectors. So this is probably more like what you are after:
vector1 <- 1:5 # just making vector of 5 numbers
vector2 <- 5:1 # same vector backwards
l <- list(Forward=vector1, Backwards=vector2) # producing list with two elements
x = "Forward"
l[!(names(l) %in% x)]
where names(l) %in% x 返回一个布尔向量，沿着列表的名称 l 指示它们是否包含在 x 中> 与否.最后，我避免使用 list 作为变量，因为你可以看到它也是一个相当常见的函数.
where names(l) %in% x returns a boolean vector along the names of the list l indicating whether they are contained in x or not. Finally, I avoided the use of list as a variable, since you can see it is a fairly common function as well.
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