Install dependencies

sudo apt-get install \
    g++ \
    gfortran \
    libcurl4-openssl-dev \
    libssh2-1-dev \
    libssl-dev \
    libxml2-dev

Install Git

curl -s https://packagecloud.io/install/repositories/github/git-lfs/script.deb.sh | sudo bash
sudo apt-get install git git-lfs
git lfs install

Add the CRAN GPG key, which is used to sign the R packages for security.

sudo apt-key adv \
    --keyserver keyserver.ubuntu.com \
    --recv-keys E084DAB9

Append the CRAN repository to sources.list.

sudo sh -c 'echo "deb https://cran.rstudio.com/bin/linux/ubuntu/ trusty/" >> /etc/apt/sources.list'

Install the latest version of R.

sudo apt-get update
sudo apt-get install r-base

Create a file named .Xmodmap:

pointer = 1 2 3 5 4 6 7 8 9 10 11 12

Note that 4 and 5 are flipped here – this enables reverse vertical scrolling.