UA Research Computing

HPC Examples


In this example, we’ll create an R script that generates 1000 randomized 1s and 0s, stores them as a dataframe, then saves the dataframe to an output file. We’ll run this R script as an array job to simulate what a researcher might do if they were performing multiple independent simulations using the same R script.

Since we’re using the same file for each simulation, if we were to create a single static output filename for our save() command, each simulation would overwrite the one that came before it. To deal with this issue, we’ll make use of the SLURM environment variable $SLURM_ARRAY_TASK_ID to differentiate them.

As a note: if you haven’t worked with array jobs before, Basic Array Jobs is a great place to get started and provides more in-depth information on their use.

R Script

This script is designed to be excuted using the following syntax:

Rscript r_array_example.R $SLURM_ARRAY_TASK_ID

The use of commandArgs() is to pull in that task ID to our R script so that we can use it in our output filenames.

# We'll pull in any command line arguments used in executing this script.
# This is to grab the SLURM_ARRAY_TASK_ID that's associated with this particular
# array subjob. We'll use this integer to differentiate save files so multiple
# simulations don't overwrite one another.

# An example of a workflow is included below

# Generate sample of 1000 random 0s and 1s
a <-sample(0:1, 1000, rep = TRUE)
# Save as data.fame
df <- data.frame(replicate(10,sample(0:1,1000,rep=TRUE)))

# Now we'll save our dataframe to a unique filename. If we run our job with:
# Rscript r_array_example.R $SLURM_ARRAY_TASK_ID
# then args[1] will be set to the job's unique integer. Using paste, we can
# add this into our save filename.
filename <- paste("random_sample_df_run", args[1], ".rda", sep = "", collapse = NULL)

# For demonstration purposes, we'll print out the expected filename
sprintf("Simulation complete. Saving dataframe to filename: %s", filename)

save(df, file = filename)

Submission Script

#SBATCH --account=your_group_here
#SBATCH --partition=standard
#SBATCH --time=00:01:00
#SBATCH --ntasks=1
#SBATCH --nodes=1
#SBATCH --array=1-2

module load R/4.1.0

Rscript save_example.R $SLURM_ARRAY_TASK_ID

Job Submission

[netid@cpu4 ~]$ sbatch r_array_example.slurm 
Submitted batch job 260764


[netid@cpu4 ~]$ cat slurm-260764_* | grep Simulation
[1] "Simulation complete. Saving dataframe to filename: random_sample_df_run1.rda"
[1] "Simulation complete. Saving dataframe to filename: random_sample_df_run2.rda"
[netid@cpu4 ~]$ ls random_sample_df_run*
random_sample_df_run1.rda  random_sample_df_run2.rda