GAMS + R Markdown scripting

In [1] I discussed a small script that exported GAMS data to R for plotting. Here I expand on that and show how we can use R Markdown [2] to generate documents that contain GAMS data and results. Here we have just a small example with just a parameter. But it is easy to see that this can also be used with larger models, where we have a document built around more complex model results. 

R Markdown can handle as input text, R code, R graphics and LaTeX math (among others). Output can be HTML, PDF (via LaTeX), and DOCX (MS Word).

Here is my example:

$ontext    Generate data in GAMS and produce a document in Rmarkdown. $offtext *--------------------------------------------------- * generate some random data points *--------------------------------------------------- set    i 'points' /p1*p70/    c 'coordinates' /x,y/ ; parameter p(i,c) 'points'; p(i,c) = uniform(0,100); display p; *--------------------------------------------------- * make document *--------------------------------------------------- * GAMS macros $set script     script.R $set gdx        data.gdx $set doc_in     document.Rmd * Output file is .html,.pdf, or .docx $set doc_out    document.pdf $set plottitle    data points $set rcommand   '"c:\Program Files\R\R-4.0.3\bin\Rscript.exe" --vanilla %script%' $set pandocdir  c:/Program Files/rstudio/bin/pandoc * create gdx file with data execute_unload "%gdx%",p; * run the R script execute '%rcommand%'; * launch a pdf viewer to show the result execute 'shellexecute %doc_out%'; *--------------------------------------------------- * R script *--------------------------------------------------- $onecho > %script% options(echo=TRUE) library(rmarkdown) rmarkdown::find_pandoc(dir="%pandocdir%") rmarkdown::pandoc_version() format = switch(tools::file_ext("%doc_out%"),               "html" = "html_document",               "docx" = "word_document",               "pdf"  = "pdf_document") if (is.null(format)) stop("unknown output format") rmarkdown::render("%doc_in%",                   output_file="%doc_out%",                   output_format = format) $offecho *--------------------------------------------------- * RMarkdown document *--------------------------------------------------- $onecho > %doc_in% --- title: "Small demo" author: "Erwin Kalvelagen" date: "%system.date%" output:   pdf_document: default   html_document: default   word_document: default --- ```{r setup, include=FALSE} knitr::opts_chunk$set(echo = FALSE) library(tidyverse)  # includes ggplot library(pander)     # tables library(gdxrrw)     # read gdx file ``` In this example, we read data from GAMS. The data is from the uniform distribution:  $$     p_i \sim U(0,100)  $$ A plot can look like this: ```{r plot, echo=FALSE} # read parameter p from GDX file p <- rgdx.param("%gdx%","p") # convert from long to wide format. x,y as columns. p2 <- pivot_wider(p,id_cols=i,names_from=c,values_from=p) ggplot(p2, aes(x=x,y=y)) + geom_point() + ggtitle("%plottitle%") ``` There are facilities to create good looking tables. ```{r table1, echo=FALSE, message=FALSE, warnings=FALSE, results='asis'} set.caption("A few records from the GAMS parameter") pander(head(p2)) ``` $offecho

This GAMS file has three parts:

• GAMS code to generate some data and to execute the R script
• R code to run the R Markdown process
• R Markdown code

Notes

1. pandoc is a document translation system used by markdown. It comes with RStudio. That is the version I am using here.
2. The output type is determined by the extension specified in doc_out.
3. rmarkdown::render is the workhorse of the document creation process.
4. After generating the document, it will be opened by shellexecute.

The LaTeX/pdf output looks like:

The advantage of this setup is that we can produce good looking reports basically automatically. Just run the GAMS model and get a report with the results.

References

1. GAMS + R scripting, http://yetanothermathprogrammingconsultant.blogspot.com/2020/12/gams-r-scripting.html
2. Yihui Xie and J.J. Allaire and Garrett Grolemund (2018). R Markdown: The Definitive Guide. Chapman and Hall/CRC.