在函数中使用全局变量 [英] Using global variable in function

问题描述

我有一个非常大的数据集，并使用R对其进行了分析.

I have a very big dataset and I analyze it with R.

问题是我想在数据集中添加一些具有不同处理方式的列，并且需要一些使用某些全局变量的递归函数.每个函数修改一些全局变量并创建一些变量.因此，在内存中复制我的数据集是一个大问题...

The problem is that I want to add some columns with different treatments on my dataset AND I need some recursive function which use some global variable. Each function modify some global variable et create some variables. So the duplication of my dataset in memory is a big problem...

我阅读了一些文档:如果我没有误会，使用<<-和assign()都不会帮助我...

I read some documentation: if I didn't misunderstand, neither the use of <<- nor assign() could help me...

我想要什么:

mydata <- list(read.table(), ...)
myfunction <- function(var1, var2) {
   #modification of global mydata
   mydata = ...
   #definition of another variable with the new mydata
   var3 <- ...
   #recursive function
   mydata = myfunction(var2, var3)
}

您对我的问题有什么建议吗?

Do you have some suggestions for my problem?

推荐答案

<<-和assign均可使用:

myfunction <- function(var1, var2) {
   # Modification of global mydata
   mydata <<- ...
   # Alternatively:
   #assign('mydata', ..., globalenv())

   # Assign locally as well
   mydata <- mydata

   # Definition of another variable with the new mydata
   var3 <- ...

   # Recursive function
   mydata = myfunction(var2, var3)
}

也就是说，要想从一个函数中修改全局数据几乎总是一个坏主意，并且几乎肯定有一个更优雅的解决方案.

That said, it’s almost always a bad idea to want to modify global data from a function, and there’s almost certainly a more elegant solution to this.

此外，请注意，<<-实际上与在globalenv()中分配给变量不同，而是在父范围中分配给变量，无论可能是什么.对于在全局环境中定义的功能，它是全局环境.对于在其他地方定义的功能，它不是全局环境.

Furthermore, note that <<- is actually not the same as assigning to a variable in globalenv(), rather, it assigns to a variable in the parent scope, whatever that may be. For functions defined in the global environment, it’s the global environment. For functions defined elsewhere, it’s not the global environment.

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