how to load a library dynamically? [duplicate]

Question

Sorry for asking easy question. I am a R beginner. I tried to load a library run-time, e.g.

x<-"snow"; library(eval(x))

Result:

Error in library(eval(x)) : 'package' must be of length 1.

I would appreciate it if anyone gave me some solutions.

Answer 1

Use character.only=TRUE. See the help page for library, with ?library.

> library(x, character.only=TRUE)

Answer 2

I'd recommend to use require instead of library.

• require returns a logical indicating whether the package was successfully loaded, i.e. you can use it in constructs like

  if (require (x, character.only = TRUE))
      ...
  

  On contrast, library will by default stop with an error if the package is not available (you can change this behaviour by logical.return = TRUE, though).

• In case the package is loaded already, and this part of code is executed often, speed may matter: require is almost 20x faster than library on my laptop if the package is loaded already. If not, it calls library.