将参数传递给函数 [英] Pass arguments to function

问题描述

我在将参数传递给 R 中的函数时遇到了理解问题.

在以下示例中，我按名称从命名列表中检索值.当我直接执行时，它返回值.但是当我将相同的代码放入一个函数时，它返回 NULL.这里发生了什么?

提前致谢，米尔科

namedlist <- list(a=c("50", "80"), b=c("50"))命名列表$a# 返回: [1] "50" "80"myfunction <- function(arg){ namedlist$arg }我的功能(一)# 返回:NULL

解决方案

您正在请求:

namedlist$arg

当然，namedlist 中没有名为 "arg" 的组件，因此返回值 NULL.

这种类型的子集列表将起作用:

myfunction <- function(arg) {命名列表[[arg]]}

并返回与namedlist$a相同的值，但您确实需要将组件名称作为字符串传递:

>命名列表$a[1] "50" "80">我的功能(一)myfunction(a) 中的错误:找不到对象a">我的功能(一个")[1] "50" "80"

I have an understanding problem with passing arguments to a function in R.

In the following example, I retrieve a value from a named list by name. When I do it directly, it returns the value. But when I put the same code into a function, it returns NULL. What happens here?

Thanks in advance, Mirko

namedlist <- list(a=c("50", "80"), b=c("50")) 

namedlist$a
# returns: [1] "50" "80"

myfunction <- function(arg){ namedlist$arg }
myfunction(a)
# returns: NULL

解决方案

You are requesting:

namedlist$arg

and of course there isn't a component with the name "arg" in namedlist, hence the return value NULL.

this type of subsetting the list will work:

myfunction <- function(arg) {
    namedlist[[arg]]
}

and returns the same as namedlist$a, but you do need to pass the component name as a string:

> namedlist$a
[1] "50" "80"
> myfunction(a)
Error in myfunction(a) : object 'a' not found
> myfunction("a")
[1] "50" "80"

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