在R中使用函数参数定义全局变量 [英] Define global variable using function argument in R

问题描述

我试图在R中编写一个函数，它从数据框中删除列，并返回一个名称为函数参数的新数据：

<$ （my.data，col，new.data）{
new.data<< - my.data [， - col]
return（new.data）
}

所以在上面的例子中，我想要一个新的数据框在调用函数后存在，该函数被命名为用户输入的第三个参数。

当我调用函数时，返回正确的数据框，但那么如果我然后尝试在全局环境中使用新的数据框，我会得到 object not found 。我想通过使用全局定义 new.data 的<< - 运算符。

有人可以帮助我了解发生了什么事，并且是否有办法实现这一目标？

我发现这和

>使用 assign（）函数。

  assign（new.data，my.data [， -  col]，envir = .GlobalEnv）
  

第一个参数应该是一个字符串。在这种情况下，生成的全局变量将被命名为new.data。如果 new.data 是名称本身，请从函数调用中删除引号。

<< - 并不总是分配给全局环境。一般来说，最好从函数中返回一些东西，而不是从函数内部设置全局变量。后者更难调试。

I'm trying to write a function in R that drops columns from a data frame and returns the new data with a name specified as an argument of the function:

drop <- function(my.data,col,new.data) {
new.data <<- my.data[,-col] 
return(new.data)
}

So in the above example, I want a new data frame to exist after the function is called that is named whatever the user inputs as the third argument.

When I call the function the correct data frame is returned, but then if I then try to use the new data frame in the global environment I get object not found. I thought by using the <<- operator I was defining new.data globally.

Can someone help me understand what's going on and if there is a way to accomplish this?

I found this and this that seemed related, but neither quite answered my question.

解决方案

Use the assign() function.

  assign("new.data", my.data[,-col], envir = .GlobalEnv) 

The first argument should be a string. In this case, the resultant global variable will be named "new.data". If new.data is the name itself, drop the quotes from the function call.

<<- does not always assign to the global environment.

In general, however, it is better to return things from a function than set global variables from inside a function. The latter is a lot harder to debug.

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