Initial commit for packrat installation in R

Languages/R/Packrat_for_R.md

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+# Using Packrat environment in R 
+
+This document provides you with necessary steps to set up a Packrat
+environment in R that will allow you to install the desired R packages
+in an isolated, portable, and reproducible way. Packrat is a
+dependency management system for projects and their R package
+[dependencies](https://cran.r-project.org/web/packages/packrat/index.html). Packrat
+can be easily setup in R using its command line interface (cli) or the
+[OpenOnDemand VDI portal](https://rcood.rc.fas.harvard.edu).
+
+The steps below are applicable for both types of interfaces. For more
+information on packrat and its walkthrough guide, see [rstudio
+packrat](https://rstudio.github.io/packrat/).
+
+## Setting up Packrat and installing an R package using that
+
+Complete the below steps to install Packrat and use that to install an R package:
+
+* Go to a compute node, if on cli:
+```bash
+salloc -p test -t 60 -n1 --mem 4000
+```
+
+* Load the required R module, if on cli. On the RStudio app on VDI,
+  the R module is loaded in the form:
+```bash
+module load R/4.3.1-fasrc01
+```
+
+* Set up a local [R library](https://docs.rc.fas.harvard.edu/kb/r-packages/):
+```bash
+mkdir $HOME/apps/R_4.3.1
+export R_LIBS_USER=$HOME/apps/R_4.3.1:$R_LIBS_USER 
+```
+
+* Create a Packrat project directory:
+```bash
+cd $HOME/apps/R_4.3.1
+mkdir packrat_r
+```
+
+* Start R, if on cli, and install Packrat:
+```R
+# --- Install Packrat in R ---
+install.packages("packrat")
+# --- Choose 70 for CRAN mirror ---
+```
+
+* Initialize the Packrat project:
+```bash
+packrat::init("~/apps/R_4.3.1/packrat_r")
+```
+
+* Use snapshot feature to save changes in Packrat:
+```bash
+packrat::snapshot() 
+```
+* Check the status of Packrat:
+```bash
+packrat::status()
+```
+
+* Turn Packrat on and ensure that the directory path shown matches
+  with the desired Packrat project location:
+```bash
+packrat::on()
+```
+
+* Install the desired R package into your Packrat location, e.g.:
+```bash
+install.packages(“viridis”)
+```