r - 为什么 R 包会加载随机数？

Question

最近，我正在阅读 caret 的文档。当我注意到这一点时打包:

Also, please note that some packages load random numbers when loaded (directly or via namespace) and this may effect [sic] reproducibility.

加载随机数的包有哪些可能的用例？这似乎与可重复研究的想法背道而驰，可能会干扰我自己对 set.seed 的尝试。 . (我已经开始将种子设置为更接近需要随机数生成的代码，因为我担心加载包的副作用。)

Answer 1

执行此操作的包的一个示例是 ggplot2 ，正如 Hadley Wickham 所提到的回应 GitHub issue相关 tidyverse .

当包裹被附加时，会随机选择一个提示以显示给用户(并且有一定的概率，不显示提示)。如果我们检查它的 .onAttach()功能 as it existed before January 2018 ，我们看到它同时调用 runif()和 sample() ，改变种子:

.onAttach <- function(...) {
  if (!interactive() || stats::runif(1) > 0.1) return()

  tips <- c(
    "Need help? Try the ggplot2 mailing list: http://groups.google.com/group/ggplot2.",
    "Find out what's changed in ggplot2 at http://github.com/tidyverse/ggplot2/releases.",
    "Use suppressPackageStartupMessages() to eliminate package startup messages.",
    "Stackoverflow is a great place to get help: http://stackoverflow.com/tags/ggplot2.",
    "Need help getting started? Try the cookbook for R: http://www.cookbook-r.com/Graphs/",
    "Want to understand how all the pieces fit together? Buy the ggplot2 book: http://ggplot2.org/book/"
  )

  tip <- sample(tips, 1)
  packageStartupMessage(paste(strwrap(tip), collapse = "\n"))
}

release_questions <- function() {
  c(
    "Have you built the book?"
  )
}

然而，这已经从 been fixed提交作者 Jim Hester以便在 ggplot2 之后重置种子被附上:

.onAttach <- function(...) {
  withr::with_preserve_seed({
    if (!interactive() || stats::runif(1) > 0.1) return()

    tips <- c(
      "Need help? Try the ggplot2 mailing list: http://groups.google.com/group/ggplot2.",
      "Find out what's changed in ggplot2 at http://github.com/tidyverse/ggplot2/releases.",
      "Use suppressPackageStartupMessages() to eliminate package startup messages.",
      "Stackoverflow is a great place to get help: http://stackoverflow.com/tags/ggplot2.",
      "Need help getting started? Try the cookbook for R: http://www.cookbook-r.com/Graphs/",
      "Want to understand how all the pieces fit together? Buy the ggplot2 book: http://ggplot2.org/book/"
      )

    tip <- sample(tips, 1)
    packageStartupMessage(paste(strwrap(tip), collapse = "\n"))
  })
}

因此，包执行此操作的原因可能有多种，尽管包作者可以通过多种方式防止这种情况给用户带来意外后果。