GAMS + R Markdown scripting

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   Generate data in GAMS and produce a document in Rmarkdown.

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*---------------------------------------------------
* 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)
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*---------------------------------------------------
* 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))
```
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