How can I tell if a certain package was already installed?

Question

When I install the yaml package, an annoying error message pops up in RStudio if it had been previously installed. How can I tell if the package was already installed so I can d

Answer 1

Alternatively, you can use the require function. It will try to load the package and silently return a logical stating whether or not the package is available. There is also a warning if the package cannot be loaded.

test1 <- require("stats")
test1

test2 <- require("blah")
test2