使用省略号将参数传递给函数，并为不存在的参数设置默认值

I have a main function which passes arguments to another function which uses rpart to generate model. I would like to have the possibility to specify rpart.control from main function using ellipsis. In case when no cp or minbucket is defined, then I would like to use my default values for these two parameters.

我有一个主函数，它将参数传递给另一个函数，该函数使用rpart生成模型。我想有可能指定rpart。用省略号控制主功能。如果没有定义cp或minbucket，那么我想对这两个参数使用默认值。

So far, I was not successful - see my draft below. Currently the function is complaining that no cp is found. I understand why, but cannot figure out, how to apply defaults if user did not provide own controls.

到目前为止，我还没有成功——请看下面我的草稿。目前函数正在抱怨没有找到cp。我理解为什么，但不能理解，如果用户没有提供自己的控件，如何应用默认值。

require(rpart)

a <- function(df, ...) {
  b(df, ...)
}

b <- function(df, ...) {
  if (is.null(cp)) cp <- 0.001 
  if (is.null(minbucket)) minbucket = nrow(df) / 20
  rcontrol <- rpart.control(cp = cp, minbucket = minbucket, ...)
  rcontrol
}


a(iris) # no controls set my defaults for cp and minbucket
a(iris, cp = 0.123) # set cp, use my default for minbucket
a(iris, cp = 0.123, minbucket = 100) # set cp, and minbucket
a(iris, maxcompete = 3) # use my defaults for cp and minbucket, but pass maxcompete

2 个解决方案

#1

Here's a small correction to your function: apply list(...) first.

这里是对你的函数的一个小更正:应用列表(…)

b <- function(df, ...) {
  l <- list(...)
  if (is.null(l$cp)) l$cp <- 1
  if (is.null(l$minbucket)) l$minbucket <- 2
  print_all(l$cp, l$minbucket, ...)
}

print_all <- function(...) {
  print(list(...))
}

Run your examples to make sure all defaults are set.

运行示例，确保设置了所有默认值。

#2

this might work for you

这可能对你有用

a <- function(df, cp = NULL, minbucket = NULL, ...) {
  if (is.null(cp)) cp <- 0.001
  if (is.null(minbucket)) minbucket <- nrow(df) / 20

  rpart.control(cp = cp, minbucket = minbucket, ...)  
}

good source for more infos (Advanced R by Hadley Wickham) http://adv-r.had.co.nz/Functions.html

获取更多信息的好来源(哈德利·韦翰的高级R) http://adv-r.had.co.nz/Functions.html

#1