如何在R中引用函数中的局部环境? [英] How can I reference the local environment within a function, in R?

问题描述

[此问题已由Spacedman在聊天室中解决，但我要发布以便将来为他人谋取利益.]

[This question has been resolved in the chat room, by Spacedman, but I'm posting it for others' benefit in the future.]

我有一个函数myFunc，可在其中创建localFunc. (注意:这不是在程序包中，而是在全局环境中.)我想知道localFunc在搜索路径中的位置，因为我想通过mvbutils::foodweb对其进行分析.

I have a function, myFunc, which creates localFunc inside of it. (NB: this is not in a package, but in the global environment.) I'd like to know where localFunc exists in the search path, as I'd like to analyze it via mvbutils::foodweb.

这里是一个例子:

myFunc <- function(){
    require(data.table)
    require(mvbutils)
    localFunc <- function(x){
        return(as.data.table(x))
    }

    vecPrune <- c("localFunc",ls("package:data.table"))
    ix <- match("data.table",search())
    tmpWeb <- foodweb(where = c(1,ix), prune = vecPrune, plotting = FALSE)
    return(tmpWeb)
}

但是，对myFunc()的调用似乎并不表示localFunc会调用data.table().这是不正确的-有什么作用?

However, a call to myFunc() does not seem to indicate that localFunc calls data.table(). This is incorrect - what gives?

(注意:where参数指定搜索路径.)

(NB: The where argument specifies the search path.)

更新1:正如Tommy和Spacedman指出的那样，诀窍是指定environment().对foodweb()的调用指的是where = c(1, ix).索引1是一个错误.这是由于认为.GlobalEnv(通常是(总是?)search()向量中的第一项)是正确的搜索位置而引起的.那是错误的.相反，应该参考environment()，下面是正确的调用. (注意:ix指定data.table()在search()输出中的位置.)

Update 1: As Tommy and Spacedman point out, the trick is to specify environment(). The call to foodweb() refers to where = c(1, ix). The index 1 is a mistake. That arose from thinking that .GlobalEnv, which is often (always?) the first item in the search() vector, is the right place to search. That is erroneous. Instead, one should refer to environment(), and the correct call is below. (NB: ix specifies the location of data.table() in the search() output.)

tmpWeb <- foodweb(where = c(environment(),ix), prune = vecPrune, plotting = FALSE)

此问题出现在checkScriptDependencies函数的此问题的答案中，该函数将代码从将R脚本文件转换为本地函数，然后由foodweb分析.这是一个如何使用environment()的有限示例，Tommy已很好地说明了如何使用environment()和类似的功能.

This appears in the answer to this question, in a function called checkScriptDependencies, which wraps the code from an R script file into a local function, which is then analyzed by foodweb. This is a limited example of how to use environment(), and Tommy has given a good explanation of how to use it and similar functions in this context.

推荐答案

要获取当前环境，只需调用environment().

To get the current environment, just call environment().

通常，sys.frame返回当前在调用堆栈上的任何环境，而sys.nframe返回当前在调用堆栈上的深度. sys.frames返回调用堆栈上所有环境的列表.

In general, sys.frame returns any of the environments currently on the call stack, and sys.nframe returns the current depth of the call stack. sys.frames returns a list of all environments on the call stack.

environment(f)返回函数f的关闭环境(它将在其中查找函数和全局变量).

environment(f) returns the closure environment for a function f (where it will look for functions and global variables).

parent.env(e)返回父环境，如果在e中未找到符号，它将查找该父环境.

parent.env(e) returns the parent environment where it will look if a symbol is not found in e.

f <- function() {
  function() list(curEnv=environment(), parent=parent.env(environment()), 
          grandParent=parent.env(parent.env(environment())), callStack=sys.frames(), 
          callStackDepth=sys.nframe())
}
g <- function(f, n=2) if (n>2) g(f, n-1) else f()

floc <- f() # generate a local function
g(floc, 3) # call it

这将调用堆栈深度为3的本地函数floc.它返回一个列表，其中包含当前环境，其父级(f中的本地环境)和其父级父级(其中f为定义，因此globalenv).它还返回堆栈框架(环境)的列表.这些是g中的递归调用的环境(最后一个除外，这是floc的当前环境).

This will call the local function floc with a stack depth of 3. It returns a list with the current environment, it's parent (the local environment in f), and it's grand parent (where f was defined, so globalenv). It also returns the list of stack frames (environments). These are the environments for the recursive calls in g (except the last one which is the current environment of floc).

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