函数内部的attach()

发布于 2024-11-03 15:53:21 字数 304 浏览 2 评论 0原文

我想为函数提供 params 参数，然后附加它，以便每次引用列表元素 a 时都可以使用 a 而不是 params$a 。

run.simulation<-function(model,params){
attach(params)
#
# Use elements of params as parameters in a simulation
detach(params)
}

这有问题吗？如果我定义了一个名为 c 的全局变量，并且还定义了列表 "params" 中一个名为 c 的元素，那么在附加命令之后将使用其值？

原文

I'd like to give a params argument to a function and then attach it so that I can use a instead of params$a everytime I refer to the list element a.

run.simulation<-function(model,params){
attach(params)
#
# Use elements of params as parameters in a simulation
detach(params)
}

Is there a problem with this? If I have defined a global variable named c and have also defined an element named c of the list "params" , whose value would be used after the attach command?

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梦情居士 2024-11-10 15:53:21

Noah 已经指出使用 Attach 是一个坏主意，即使您在一些示例和书籍中看到它。有办法解决。您可以使用名为 with 的“本地附加”。在诺亚的虚拟示例中，这看起来

with(params, print(a))

会产生相同的结果，但更整洁。

Noah has already pointed out that using attach is a bad idea, even though you see it in some examples and books. There is a way around. You can use "local attach" that's called with. In Noah's dummy example, this would look like

with(params, print(a))

which will yield identical result, but is tidier.

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不再见 2024-11-10 15:53:21

另一种可能性是：

run.simulation <- function(model, params){
    # Assume params is a list of parameters from 
    # "params <- list(name1=value1, name2=value2, etc.)"
    for (v in 1:length(params)) assign(names(params)[v], params[[v]])
    # Use elements of params as parameters in a simulation
}

Another possibility is:

run.simulation <- function(model, params){
    # Assume params is a list of parameters from 
    # "params <- list(name1=value1, name2=value2, etc.)"
    for (v in 1:length(params)) assign(names(params)[v], params[[v]])
    # Use elements of params as parameters in a simulation
}

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残疾 2024-11-10 15:53:21

解决此类范围问题的最简单方法通常是尝试一些简单的方法：

a = 1
params = c()
params$a = 2
myfun <- function(params) {
  attach(params)
  print(a)
  detach(params)
}
myfun(params)

以下对象被 _by_ .GlobalEnv 屏蔽：
一个

# [1] 1

如您所见，R 在此处选取全局属性 a。

尽可能避免使用 attach 和 detach 几乎总是一个好主意——作用域最终会变得很难处理（顺便说一句，最好避免命名变量 c——R 通常会弄清楚你所指的是什么，但是还有很多其他字母，为什么要冒险呢？）。此外，我发现使用附加/分离的代码几乎无法破译。

Easiest way to solve scope problems like this is usually to try something simple out:

a = 1
params = c()
params$a = 2
myfun <- function(params) {
  attach(params)
  print(a)
  detach(params)
}
myfun(params)

The following object(s) are masked _by_ .GlobalEnv:
a

# [1] 1

As you can see, R is picking up the global attribute a here.

It's almost always a good idea to avoid using attach and detach wherever possible -- scope ends up being tricky to handle (incidentally, it's also best to avoid naming variables c -- R will often figure out what you're referring to, but there are so many other letters out there, why risk it?). In addition, I find code using attach/detach almost impossible to decipher.

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