Using R on the command line

Last updated on 2024-03-12 | Edit this page

Estimated time 12 minutes

Overview

Questions

  • How do you run R on the HPCC through the command line?
  • How can I create plots when I’m not using a graphical interface?

Objectives

  • Demonstrate how to find and load a desired version of R using the module system
  • Demonstrate how to start an R console
  • Demonstrate how to run R scripts with the RScript command

Accessing the HPCC through the terminal

Up to now, we’ve been using RStudio through OnDemand to write and run R code on the HPCC. Now, we’ll do the same things we’ve been doing, but solely through the command line. This will allow us to eventually submit SLURM batch scripts to run our code on compute nodes.

For now, we’ll start by running everything on a development node. Using our previous instructions to SSH into a development node, we can get a command line running on a development node. As a reminder, from a personal terminal, this looks something like

BASH 

ssh <netid>@hpcc.msu.edu
ssh <dev-node>

For best results, choose a development node with low usage.

Loading R

The command to run an R console from the command line is just R! But if we try it out right away, we get an error

BASH 

R

OUTPUT 

-bash: R: command not found

The HPCC packages up all of its available software into modules so that not every piece of software is available to everyone all of the time. To get access to R, we have to load its module.

Let’s first start by finding the version we’re interested in. We’ll use the module spider command which searches through all the modules for the ones we want:

BASH 

module spider R

OUTPUT 

------------------------------------------------------------------------------
  R:
------------------------------------------------------------------------------
    Description:
      R is a free software environment for statistical computing and graphics.

     Versions:
        R/3.3.1
        ...
        R/4.0.2
        R/4.0.3
        R/4.1.0
        R/4.1.2
        R/4.2.2
     Other possible modules matches:
        ADMIXTURE  AMDuProf  APR  APR-util  Abaqus_parallel  AdapterRemoval  
        Advisor  Amber  AmrPlusPlus  Archive-Zip  Armadillo  Arrow  ...

------------------------------------------------------------------------------
  To find other possible module matches execute:

      $ module -r spider '.*R.*'

We’ve abbreviated the output, but we can see that there are lots of different versions of R available! We’ll try loading 4.0.3 since that version on the HPCC has a large number of packages pre-installed.

If you’re familiar with the module system, you might try to load the module right away with module load:

BASH 

module load R/4.0.3

OUTPUT 

Lmod has detected the following error:  These module(s) or extension(s) exist
but cannot be loaded as requested: "R/4.0.3"
   Try: "module spider R/4.0.3" to see how to load the module(s).

But we get an error! Let’s try the suggested fix to see what’s going on:

BASH 

module spider R/4.0.3

OUTPUT 

----------------------------------------------------------------------------
  R: R/4.0.3
----------------------------------------------------------------------------
    Description:
      R is a free software environment for statistical computing and
      graphics.


    You will need to load all module(s) on any one of the lines below before the
    "R/4.0.3" module is available to load.

      GCC/10.2.0  OpenMPI/4.0.5
      GCC/9.3.0  OpenMPI/4.0.3
      iccifort/2020.1.217  impi/2019.7.217
 
    Help:
      Description
      ===========
      R is a free software environment for statistical computing
       and graphics.
    ...

Ah-ha! We see that we need to load some other modules first! These are dependencies that R needs to run. Without them, it won’t work!

Before we do that, it’s good practice to purge any other modules that might be loaded that we won’t need. This will ensure a clean environment and will reduce the possibility of any conflicts.

BASH 

module purge
module load GCC/10.2.0 OpenMPI/4.0.5 R/4.0.3

No error! Let’s check that we can access R:

BASH 

R

OUTPUT 

R version 4.0.3 (2020-10-10) -- "Bunny-Wunnies Freak Out"
Copyright (C) 2020 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.

  Natural language support but running in an English locale

R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.

Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

>

Great! We now have an R console where we can run short lines of code, just like from RStudio. As the output from R shows, type q() to quit and return back to the command line.

If you’re asked to save the workspace image, it’s best practice to say no since this can lead to long load times and less reproducible sessions in the future. In fact, you can use the --vanilla option when starting R to ensure it ignores things like your .Renviron and .Rprofile changes. We will use this option below to make sure we run our code in the cleanest environment possible.

Running one-liners and scripts with RScript

The R console is great for interactive work. But sometimes we might want to just send some code to R to run and give us back the answer. For this, we use the Rscript command.

First, let’s start by sending Rscript a single command using the -e flag (which stands for “expression”):

BASH 

Rscript --vanilla -e 'date()'

OUTPUT 

[1] "Wed Jun 14 15:20:58 2023"

We get the same output as if we had run date() in an R console or in a script! Note that we have to wrap the expression we want to run in single quotes.

We can run multiple expressions at once. For example, let’s get the quotient and remainder of 128 divided by 11:

BASH 

Rscript --vanilla -e '128 %/% 11' -e '128 %% 11'

OUTPUT 

[1] 11
[1] 7

The real power of Rscript comes into play when we have an actual script to run! Let’s run our previous one. Rscript takes the path to the script as argument. We’ll first change directory to the location of our script so we don’t need to specify the entire path name.

BASH 

cd ~/r_workshop
Rscript src/test_sqrt_multisession.R

OUTPUT 

   user  system elapsed 
  0.238   0.003   1.698

This is the equivalent of clicking the Source button while we have a R script open in RStudio, or running source('~/r_workshop/src/test_sqrt_multisession.R') from an R console. Notice that we didn’t use the --vanilla option here. This ensures that we use the local library setup in the project directory.

Writing scripts that take command line arguments

Often, you will want to be able to pass extra arguments to your scripts when you run them from the command line. The simplest way is to use the commandArgs function in R which lets us access all of the command line arguments as a character vector.

From the command line, open a new R script called src/command_args.R in a text editor of your choice. If you aren’t familiar with any, a good option is nano.

BASH 

nano src/command_args.R

Our script will print out all of our command line arguments:

R 

args <- commandArgs(trailingOnly = TRUE)
nargs <- length(args)

for(i in 1:nargs) {
  cat("Argument", i, ":", args[i], "\n")
}

It’s important to use the trailingOnly = TRUE option with commandArgs so that we only get the arguments after the name of the script.

If you’re using nano, after typing the above code, press ctrl+o followed by enter to save, then ctrl+x to exit.

We can now run our script through Rscript with some arguments:

BASH 

Rscript --vanilla src/command_args.R a b c

OUTPUT 

Argument 1 : a 
Argument 2 : b 
Argument 3 : c

For a more sophisticated way to handle command line arguments (including flags, automated usage messages, default options, and more), check out optparse.

Challenge

Write an Rscript one-liner to print the numbers from 1 to 10.

BASH 

Rscript --vanilla -e 'for(i in 1:10) print(i)'

Challenge

Write an Rscript one-liner to display the help for the function strtoi (press “q” to exit).

BASH 

Rscript --vanilla -e 'help(strtoi)'

Challenge

Write an Rscript that takes an integer as a command line argument and prints the numbers from 1 to that integer.

R 

args <- commandArgs(trailingOnly = TRUE)
n <- strtoi(args[1])

for(i in 1:n) {
  print(i)
}

Plotting with the command line

You may wonder how you might run a plot using the terminal interface? For most terminals, if you plot with the command line version of R, either nothing happens or there is an error message. It may work on some terminals, if X11 Linux graphical interface is installed and the terminal is an X11-capable (for example on MacOS is ‘Quartz’ is installed, a new windows will appear). However when running in ‘batch’ mode using the cluster (described in the next session), there is no interface at all.

There are the following techniques for handling plots when using R on the command line on HPCC

  • split your code into computation and presentation sections: run computation section using CLI/Batch on HPC, and after the computation is complete, save the output to be read into visualization code that you run on a machine with a graphic user interface (OnDemand Rstudio, or even your laptop)
  • capture all output to a file using commands like PDF()
  • as part of your script, create an RMarkdown file that includes plotting (or other output), and use the render command in Rmarkdown to PDF or other format to be review later

We’ll describe the method to capture output into a PDF here.

A sample script that uses the pdf function to capture plots looks like this:

R 

plotfile = 'testplots.pdf'
pdf(plotfile)

plot(iris$Petal.Length, iris$Petal.Width, pch=21, bg=c("red","green3","blue")[unclass(iris$Species)], main="Edgar Anderson's Iris Data")

dev.off()

For much nore details about using this techinque, see Chapter 14 Output for Presentation of Winston Chang’s R Graphics Cookbook

Once you run the script and save the PDFs, the next challenge is to view them because, again, the terminal does not have the GUI to view PDFs.

You could

  • download the PDF to your computer from the terminal using OnDemand file browser (or the MobaXterm client’s file browser)
  • open with the OneDemand Rstudio.

Challenge

One of the challenges with running scripts repeatedly is that it will overwrite the plot file with the same name. Modify the plotting script above that accepts a command line parameter for the the name of the PDF file. BONUS: how would you handle the case where there was no command line argument sent?

R 

args <- commandArgs(trailingOnly = TRUE)

# check if there was at least 1 arg
if length(args) >= 1 {

   #assume the arg is a PDF file name, and use that to capture plots
   plotfile = args[1]
   pdf(plotfile)

}

# if not argument is sent, PDF capture is not enabled and the plot will display

plot(iris$Petal.Length, iris$Petal.Width, pch=21, bg=c("red","green3","blue")[unclass(iris$Species)], main="Edgar Anderson's Iris Data")

dev.off()

Key Points

  • Use module spider R/<version> to learn how to load a version of R on the HPCC
  • Run R from the command line to start an interactive R console
  • Use the --vanilla option to ignore extra configuration files
  • Run Rscript to run an R script
  • Use commandArgs to parse command line arguments in an R script
  • Use pdf() to capture plotting into a PDF file