r - 在 R 中使用 NSE 生成信息丰富的 `stopifnot()` 错误

Question

我想要提供信息丰富的 stopifnot() 错误。

我读过: http://r-pkgs.had.co.nz/tests.html (最后关于使用 NSE 为示例打印出信息性测试错误的部分似乎相关) 和 http://adv-r.had.co.nz/Computing-on-the-language.html 但我不能让它在简洁的代码中打印一个信息性错误:

e <- new.env()
e$label <- c(1,2,3)
check_in_y <- function(x, z, e) {
  stopifnot(eval(bquote(.(x) %in% e[[.(z)]])))
}

check_in_y(5,"label", e)

输出给出了这个(信息量不大)

Error: eval(bquote(.(x) %in% e[[.(z)]])) is not TRUE

我希望错误信息更丰富，这样说:

Error: 5 %in% e[["label"]] is not TRUE

我怎样才能让它工作？或者实现我想要的最佳方法是什么

我知道我可以编写一个 if condition not true 然后打印我自己的错误作为替代，但是额外的代码很麻烦。我想了解如何让 NSE 让它发挥作用。

编辑: 我采用这种方法的动机来自阅读 hadley 的评论(位于 http://r-pkgs.had.co.nz/tests.html):

However, if the expectation fails this doesn’t give very informative output:

expect_floor_equal("year", "2008-01-01 00:00:00")
## Error: floor_date(base, unit) not equal to as.POSIXct(time, tz = "UTC")
## Mean absolute difference: 31622400

Instead you can use a little non-standard evaluation to produce something more informative. The key is to use bquote() and eval(). In the bquote() call below, note the use of .(x) - the contents of () will be inserted into the call.

expect_floor_equal <- function(unit, time) {
  as_time <- function(x) as.POSIXct(x, tz = "UTC")
  eval(bquote(expect_equal(floor_date(base, .(unit)), as_time(.(time)))))
}
expect_floor_equal("year", "2008-01-01 00:00:00")
## Error: floor_date(base, "year") not equal to as_time("2008-01-01 00:00:00")

Answer 1

stopifnot 只是

的便利功能

if(!all(condition)) stop(standard message)

对于自定义消息，只需编写代码。您可以用两行替换 stopifnot 调用:

check_in_y <- function(x, z, e) {
    b <- bquote(.(x) %in% e[[.(z)]])
    if(!eval(b)) stop(deparse(b), " is not TRUE", call. = FALSE)
}

check_in_y(5, "label", e)
# Error: 5 %in% e[["label"]] is not TRUE