以编程方式创建目标列表时找不到对象

Question

我正在尝试通过 R 包中的函数以编程方式生成 {targets} 列表。

get_pipeline <- function(which_countries) {
  countries <- NULL # avoid R CMD CHECK warning
  print(which_countries) # Shows that which_countries is available
  list(
    targets::tar_target(
      name = countries,
      command = which_countries # But here, which_countries is not found
    )
  )
}

_targets.R 文件如下所示：

library(targets)
couns <- c("USA", "GBR")
TargetsQuestions::get_pipeline(couns)

我看到以下错误：

> tar_make()
[1] "USA" "GBR"
Error in enexpr(expr) : object 'which_countries' not found
Error in `tar_throw_run()`:
! callr subprocess failed: object 'which_countries' not found

请注意，which_countries 变量是可打印的，但在对 tar_target 的调用中找不到。

如何才能成功创建 countries 目标，使其包含向量 c("USA", "GBR")？

此代码位于 https://github.com/MatthewHeun/TargetsQuestions 的 GitHub 存储库中。重现：

git clone https://github.com/MatthewHeun/TargetsQuestions
在 RStudio 中构建包。
targets::tar_make() 在控制台。

提前感谢您的任何建议！

Answer 1

感谢@landau 指向 https://wlandau.github.io/targetopia/contributing.html#target-factories which in turn points to the metaprogramming section of Advanced R at https://adv-r.hadley.nz/metaprogramming.html。

解决方案原来是：

get_pipeline <- function(which_countries) {
  list(
    targets::tar_target_raw(
      name = "countries",
      # command = which_countries # which_countries must have length 1
      # command = !!which_countries # invalid argument type
      command = rlang::enexpr(which_countries) # Works
    )
  )
}

与 _targets.R 像这样：

library(targets)
couns <- c("USA", "GBR")
TargetsQuestions::get_pipeline(couns)

命令tar_make()和tar_read(countries)，给出

[1] "USA" "GBR"

符合预期！

以编程方式创建目标列表时找不到对象

object not found when creating targets list programmatically

targets-r-package