如何检查 R 函数的输入参数是否存在 [英] How to check existence of an input argument for R functions

问题描述

我有一个函数定义为

myFun <- function(x, y, ...) {
  # using exists
  if (exists("z")) { print("exists z!") }
  # using missing
  try(if (!missing("z")) { print("z is not missing!") }, silent = TRUE)
  # using get
  try(if (get("z")) { print("get z!") }, silent = TRUE)

  # anotherFun(...)
}

在这个函数中，我想检查用户是否在参数列表中输入了z".我怎样才能做到这一点?我尝试了 exists("z")、missing("z") 和 get("z")，但它们都不起作用.

In this function, I want to check whether user input "z" in the argument list. How can I do that? I tried exists("z"), missing("z"), and get("z") and none of them works.

推荐答案

@Sacha Epskamp 有一个很好的解决方案，但它并不总是有效.失败的情况是如果z"参数作为 NULL 传入...

@Sacha Epskamp has a pretty good solution, but it doesn't always work. The case where it fails is if the "z" argument is passed in as NULL...

# Sacha's solution
myFun <- function(x, y, ...) { 
  args <- list(...)
  exist <- !is.null(args[['z']])
  return(exist)
}

myFun(x=3, z=NULL) # FALSE, but should be TRUE!


# My variant
myFun2 <- function(x, y, ...) {
  args <- list(...)
  exist <- "z" %in% names(args)
  exist
}

myFun2(x=3, z=NULL) # TRUE

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