Warning message:
In install.packages(pkgs = doing, lib = lib, ...) :
installation of package ‘RcppArmadillo’ had non-zero exit status

install.packages("RcppArmadillo")

There is a binary version available but the source version is later:
binary source needs_compilation
RcppArmadillo 0.8.400.0.0 0.8.500.0 TRUE

Do you want to install from sources the package which needs compilation? (Yes/no/cancel) no

試開URL’https://cran.rstudio.com/bin/macosx/el-capitan/contrib/3.5/RcppArmadillo_0.8.400.0.0.tgz'
Content type 'application/x-gzip' length 1647889 bytes (1.6 MB)
==================================================
downloaded 1.6 MB

The downloaded binary packages are in
/var/folders/3r/d9836crj7bd80_nsw334wx6c0000gn/T//Rtmpfoy4Oj/downloaded_packages

library(RcppArmadillo)