Question

我希望能够有一种方法来检查所有参数，而不是在调用R中的函数时指定默认值。这对我来说似乎是一件明智的事情，因为它避免了函数在以后失败（当发现一个值丢失时，可能经过大量处理）。

完成此任务的一种方法是为每个参数编写一个if (missing(arg))语句，但这需要保持函数的参数和上述语句相互一致，所以我正在寻找一个更好的解决方案。

目前我使用以下功能，这在大多数情况下有效，但不是全部。

# check for required arguments by getting arguments for the
# definition of the calling function and comparing to the arguments 
# in the function call
check_required_args <- function () {
    def    <- sys.function(-1)
    f_args <- formals(def)
    f_args <- f_args[sapply(f_args, is.name)]  # remove arguments with defaults
    f_args <- names(f_args)
    f_args <- f_args[f_args != '...'] # remove ellipsis argument if present

    call   <- match.call(definition=def, call=sys.call(-1))
    f_name <- call[1]
    c_args <- names(as.list(call[-1]))

    for(n in f_args) {
        if (!n %in% c_args) {
            stop("Argument '", n, "' missing from call to function ", 
                f_name, "()", call.=FALSE)
        }
    }
}

f <- function(a, b, c=2) check_required_args()
f(a=1) # should fail (missing argument b)
f(2, 3) # should work
f(2, c=5) # should fail (missing argument b)
f(2, 3, 4) # should work


f <- function(a, b, ...) f2(a, b, ...)
f2 <- function(a, b, c, ...) check_required_args()

f2(a=1, b=2, c=3) # should work
f2(a=1, b=2) # should fail (missing argument c for function f2)
f(a=1, b=2, c=3) # should work
f(a=1, b=2) # should fail  (missing argument c for function f2)

是否可以改进此功能以适用于所有这些情况？如果没有，是否有更合适的解决方案来执行此检查？

Answer 1

也许这个？

check_required_args <- function (fun = sys.function(-1), ncall = 3) {
  f_args <- formals(fun)
  f_args <- f_args[vapply(f_args, is.symbol, FUN.VALUE = TRUE)]
  f_args <- names(f_args)
  f_args <- setdiff(f_args, "...")
  test <- vapply(f_args, 
                 function(x) missingArg(as.name(x), envir = parent.frame(ncall), eval = TRUE), 
                 FUN.VALUE = TRUE)
  stopifnot(!any(test))
  return(invisible(NULL))     
}


f <- function(a, b, c=2) {
  check_required_args()
  return("Hello!")
}
f(a=1) # should fail (missing argument b)
#Error: !any(test) is not TRUE

f(2, 3) # should work
#[1] "Hello!"

f(2, c=5) # should fail (missing argument b)
# Error: !any(test) is not TRUE

f(2, 3, 4) # should work
#[1] "Hello!"

x <- 1
f(a=x, 3)
#[1] "Hello!"


f <- function(a, b, ...) f2(a, b, ...)
f2 <- function(a, b, c, ...) {
  check_required_args()
  return("Hello!")
}

f2(a=1, b=2, c=3) # should work
#[1] "Hello!"

f2(a=1, b=2) # should fail (missing argument c for function f2)
#Error: !any(test) is not TRUE 

f(a=1, b=2, c=3) # should work
#[1] "Hello!"

f(a=1, b=2) # should fail  (missing argument c for function f2)
#Error: !any(test) is not TRUE

编辑：

您可能希望使用get来检查是否存在：

check_required_args <- function (fun = sys.function(-1), ncall = 3) {
  f_args <- formals(fun)
  f_args <- f_args[vapply(f_args, is.symbol, FUN.VALUE=TRUE)]
  f_args <- names(f_args)
  f_args <- setdiff(f_args, "...")
  test <- lapply(f_args, 
                 function(x) {
                   get(x, envir = parent.frame(ncall), inherits = TRUE)
                   return(NULL)
                   })
  #possibly use a for loop instead
  #wrap in tryCatch for customized error messages

}

f <- function(a, b, ...) f2(a, b, ...)
f2 <- function(a, b, c, ...) {
  check_required_args()
  return("Hello!")
}

f(c=2)
#Error in get(x, envir = parent.frame(ncall), inherits = TRUE) : 
#  argument "a" is missing, with no default

如果您不想签入封闭的框架，请设置inherits = FALSE。

R：提供检查强制/必需参数

1 个答案:

编辑：