不使用参数时运行具有多个参数的函数 [英] Running a function with multiple arguments when an argument is not used

问题描述

我认为我的问题可以变得非常普通和简单，这样我就不会给出我要实现的具体功能.

I think my question can be made quite generic and simple, so that I will not give the concrete function that I am trying to make.

我有一个根据其第一个参数更改其行为的函数:

I have a function that changes its behaviour according to its first argument:

example <- function(arg1 = T,
                    arg2 = NULL,
                    arg3,
                    ...) {
  if (arg1 != T) {

    final <- bind_rows(arg2)

  } else{
    list1 <- list(...)
    final <- bind_rows(list1, arg3)

  }


  return(final)
}

我的问题是，如果我运行 example(arg1 = T，arg3 = x，c(A，B)，c(C，D))，考虑到我函数的用户可能不会为 arg2 写任何内容，我有问题. c(A，B)最终没有被视为 list1 的第一个元素(我想它已分配给 arg2 ，然后在函数)，我有 bind_rows(c(C，D)，x)作为输出，而不是 bind_rows(c(A，B)，c(C，D)，x).

My issue is that if I run example(arg1 = T, arg3 = x, c(A,B), c(C,D)), considering that the user of my function probably won't write out anything for arg2, I have a problem. c(A,B) ends up not being considered the first element of list1 (I guess it is assigned to arg2 and then goes unused in the function) and I have bind_rows(c(C,D), x) as the output, instead of bind_rows(c(A,B), c(C,D), x).

考虑到该功能不是供个人使用，而是用于较大的包装，如何解决?

How can this be fixed, considering that the function is not for personal use, but for a larger package?

推荐答案

将arg2放入 ...

example <- function(arg1 = T,
                    arg3,
                    ...) {
  args <- list(...)
  if (is.null(args$arg2) & arg1==F) {stop("arg2 needed when arg1==F")}

  if (arg1 != T) {

    final <- list(arg2)

  } else{
    list1 <- list(...)
    final <- list(list1, arg3)

  }


  return(final)
}

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