r - 如何处理......当最后一个参数为空时？

Question

使用时 ...捕获其他参数，将最后一个参数留空并尝试使用 list(...)会产生错误

f <- function(x, ...) {
    args <- list(...)
}

f(x = 0, y = 10,)


> Error in f(x = 0, y = 10, ) : argument is missing, with no default

这里的错误消息仍然是信息性的，但如果你传递 ...你最终得到以下结果

f1 <- function(x, ...) {
    f2(x, ...)
}

f2 <- function(x, ...) {
    list(...)
}

f1(x = 0, y = 10,)

> Error in f2(x, ...) : argument is missing, with no default

现在它变得很不清楚出了什么问题。是否有惯用的技术来捕获错误并用有用的消息报告它？

Answer 1

f <- function(x, ...) {
    return(
        as.list(substitute(list(...)))[-1]
    )
}

err <- f(x = 0, y = 10,)   #have a closer look --> str(err)

#$`y`
#[1] 10
# 
#[[2]]

fine<- f(x = 0, y = 10)

#$`y`
#[1] 10

您会在 Error 案例中看到您有一个空的符号列表元素。我相信您可以将此信息用作错误处理的 Hook 。

所以你有意义的错误处理可以是这样的:

感谢@Roland 的加入。

f <- function(x, ...) {
    res <- as.list(substitute(list(...)))[-1]
    if( any(  sapply(res, function(x) { is.symbol(x) && deparse(x) == "" })  ) )  stop('Please remove the the last/tailing comma "," from your input arguments.')
    print("code can run. Hurraa")
}

a <- 0; 
f(x = 0, y = a, hehe = "", "")
#[1] "code can run. Hurraa"

f(x = 0, y = a, hehe = "", "", NULL)
#[1] "code can run. Hurraa"

f(x = 0, y = a, hehe = "", "",)
#Error in f(x = 0, y = a, hehe = "", "", ) : 
#Please remove the the last/tailing comma "," from your input arguments.

f(x = 0, y = a, hehe = "", "", NULL,)
#Error in f(x = 0, y = a, hehe = "", "", NULL, ) : 
#Please remove the the last/tailing comma "," from your input arguments.