避免被要求提供 CRAN 镜像？

Question

When running R from the terminal, we sometimes see

--- Please select a CRAN mirror for use in this session ---

Is there a universal, efficient, and memorable way to install.packages("example") without needing to memorise urls or interact with a dialogue box?

That is, is there a way to install an R package which is:

1. universal (works on any/all installations of R, irrespective of operating system)
2. Requires no memorisation of url(s)
3. Requires no interaction with duologue box(es)
4. Requires no files (eg .Rprofile ) to be created or edited

Lastly, ideally, a method which is short and memorable (or easy use without having to look it up).

Here's a pseudo code example of an ideal solution (where 'force' is pseudocode for 'choose the most obvious defaults and press on at all costs!)

force(install.packages("example"))

Answer 1

If you run help("install.packages") , you can see that the default value for the repository is repos = getOption("repos") . If you follow this trail to help("getOption") , it provides some more insight. Here is what it says for the repos option.

repos:

URLs of the repositories for use by update.packages. Defaults to c(CRAN="@CRAN@"), a value that causes some utilities to prompt for a CRAN mirror. To avoid this do set the CRAN mirror, by something like local({r <- getOption("repos"); r["CRAN"] <- "http://my.local.cran"; options(repos = r)}).

You can see this by going into the 'etc/' subdirectory of your R installation. There is a file there called 'repositories'. While some other repos (eg, R-Forge) have default URLs, CRAN does not. It shows @CRAN@ as referenced by the help file.

The R documentation advises you that some utilities, such as what you are experiencing at the command line, will prompt you for a mirror, unless the option is explicitly set. The documentation does not indicate an alternative work around.

The reason why there cannot be a function to tell it to use the "most obvious default" is that there is actually no default. So a method such as your hypothetical force() would not be possible.

---

An edit with a bit more info:

You can use a few helpers from utils to set the repos option. I am not sure if it is easy enough to remember for your criteria, but there is chooseCRANmirror() and getCRANmirrors() .

# this should work
chooseCRANmirror(ind = 1)
install.packages("example")

# or this clunky approach
install.packages("example", repos = getCRANmirrors()[1,"URL"])

But honestly at that point you may be better off just remembering repos = https://cloud.r-project.org/ .