$ sudo apt-get remove r-base 

Uninstall r-base including dependent package

If you would like to remove r-base and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove r-base 

Use Purging r-base

If you use with purge options to r-base package all the configuration and dependent packages will be removed.

$ sudo apt-get purge r-base 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove r-base 

See Also,