First add my proxy repository to your apt sources.
sudo sh -c "echo deb http://repo.colin.geek.nz/rstudio devel main > /etc/apt/sources.list.d/rstudio.list"
This repository does not host any of the RStudio packages but instead will redirect your apt client to the official packages hosted by RStudio.
You will also need to add a R repository to your apt sources. There are many mirrors, such as this one hosted by RStudio.
sudo sh -c "echo deb http://cran.rstudio.com/bin/linux/ubuntu xenial/ >> /etc/apt/sources.list.d/rstudio.list"
You will also need to add the public keys
wget -O - http://repo.colin.geek.nz/rstudio/rstudio-apt.asc | sudo apt-key add - sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E084DAB9
Now finally, install rstudio and enjoy.
sudo aptitude update sudo aptitude install rstudio