SGE array jobs and R - arrays

Question

I currently have a R script written to perform a population genetic simulation, then write a table with my results to a text file. I would like to somehow run multiple instances of this script in parallel using an array job (my University's cluster uses SGE), and when its all done I will have generated results files corresponding to each job (Results_1.txt, Results_2.txt, etc.).
Spent the better part of the afternoon reading and trying to figure out how to do this, but haven't really found anything along the lines of what I am trying to do. I was wondering if someone could provide and example or perhaps point me in the direction of something I could read to help with this.

Answer 1

To boil down mithrado's answer to the bare essentials:
Create job script, pop_gen.bash, that may or may not take SGE task id argument as input, storing results in specific file identified by same SGE task id:
#!/bin/bash
Rscript pop_gen.R ${SGE_TASK_ID} > Results_${SGE_TASK_ID}.txt
Submit this script as a job array, e.g. 1000 jobs:
qsub -t 1-1000 pop_gen.bash
Grid Engine will execute pop_gen.bash 1000 times, each time setting SGE_TASK_ID to value ranging from 1-1000.
Additionally, as mentioned above, via passing SGE_TASK_ID as command line variable to pop_gen.R you can use SGE_TASK_ID to write to output file:
args <- commandArgs(trailingOnly = TRUE)
out.file <- paste("Results_", args[1], ".txt", sep="")
# d <- "some data frame"
write.table(d, file=out.file)
HTH

Answer 2

I am not used to do this in R, but I've been using the same approach in python. Imagine that you have an script genetic_simulation.r and it has 3 parameter:
--gene_id --khmer_len and --output_file.
You will have one csv file, genetic_sim_parms.csv with n rows:
first_gene,10,/result/first_gene.txt
...
nth_gene,6,/result/nth_gene.txt
A import detail is the first lane of your genetic_simulation.r. It needs to tell which executable the cluster is going to will use. You might need to tweak its parameters as well, depending on your setup, it will look like to:
#!/path/to/Rscript --vanilla
And finally, you will need a array-job bash script:
#!/bin/bash
#$ -t 1:N < change to number of rows in genetic_sim_parms.csv
#$ -N genetic_simulation.r
echo "Starting on : $(date)"
echo "Running on node : $(hostname)"
echo "Current directory : $(pwd)"
echo "Current job ID : $JOB_ID"
echo "Current job name : $JOB_NAME"
echo "Task index number : $SGE_TASK_ID"
ID=$(awk -F, -v "line=$SGE_TASK_ID" 'NR==line {print $1}' genetic_sim_parms.csv)
LEN=$(awk -F, -v "line=$SGE_TASK_ID" 'NR==line {print $2}' genetic_sim_parms.csv)
OUTPUT=$(awk -F, -v "line=$SGE_TASK_ID" 'NR==line {print $3}' genetic_sim_parms.csv)
echo "id is: $ID"
rscript genetic_simulation.r --gene_id $ID --khmer_len $LEN --output_file $OUTPUT
echo "Finished on : $(date)"
Hope this helps!