R中函数参数的所有有效值 [英] All valid values of an argument of a function in R

问题描述

假设我们有一个 R 函数，其参数必须从有限的元素集中选择.像 qplot(..., geom="").而 geom 只能取一些值，例如 bar 或 point.

Suppose we have an R function whose arguments must be selected out of a finite set of elements. Like qplot(..., geom=""). And geom can take only some values, like bar or point.

如何找出给定函数的参数可能采用的所有有效值?除了经常错过所有可能值的文档或 Internet.也许，一些 R 函数可以提供帮助?

How can I find out all the valid values the argument of a given function may take? Apart from docs or Internet, which often miss all possible values. Perhaps, some R function can help?

推荐答案

如果感兴趣的函数是这样定义的

If the function of interest is defined like

f <- function(a = c("foo","bar")) {
    match.arg(a)
}

即when the options are defined as a vector to be later checked with match.arg function, then you could use the formals function which would give you a list of arguments with the values就像下面的例子

i.e. when the options are defined as a vector to be later checked with match.arg function, then you could use the formals function which would give you a list of arguments with the values like in the following example

> formals(f)
$a
c("foo", "bar")

否则我认为没有 RTFSing 就不可能获得所有有效的参数值.

Otherwise I don't think it is possible to get all valid argument values without RTFSing.

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