Why doesn't the table generated from r-exams appear in Moodle?

Question

I have defined the variables and data necessary to generate a frequency table in RMarkdown, to export it to Moodle, using R-exams:

xsubio<-c(sample(5:35,5))
xsubi<-sort(xsubio)
frecuencias<-sample(0:30 ,5)

tabla<-data.frame(xsubi,frecuencias)
colnames(tabla)<-c(" Edades" ,"Personas")

Through chunk I generate the table:

```{r, eval=TRUE,echo=FALSE,results='asis',warning=FALSE,message=FALSE,error=FALSE}
   library(exams)
   print(xtable(tabla), include.rownames=FALSE)
```

When exporting to PDF, using exams2pdf, the table is displayed perfectly:

But, when exporting to Moodle, using exams2moodle, the table disappears:

What do I have to do to make it appear?

Answer 1

Problem: You have an exercise with formatting in Markdown and use xtable() to insert a table in LaTeX. This mixture of Markdown+LaTeX is no problem when converting the exercise to PDF. Internally, this preserves the LaTeX table and just converts the Markdown parts to LaTeX as well before rendering the LaTeX to PDF. However, the same is not possible automatically when converting the Markdown exercise to HTML for Moodle. The converter then does not separate the LaTeX part automatically to convert it to HTML.

In short: The different markups must be sufficiently in sync. Markdown+LaTeX markup for PDF output works and Markdown+HTML for HTML output works. But what would be even better is to have the markup fully in sync, i.e., LaTeX+LaTeX or Markdown+Markdown. Such exercises can then be rendered to either PDF or HTML automatically.

Possible solutions:

1. Markdown+Markdown: Markdown table markup in R/Markdown (Rmd) exercise
   I would recommend that you simply produce tables in Markdown via knitr::kable() rather than xtable::xtable(). Thus, the code chunk for the table simply becomes

   knitr::kable(tabla, format = "markdown")
   

   and then the tables are rendered correctly in both PDF and HTML-based formats like Moodle.

2. LaTeX+LaTeX: LaTeX table markup in R/LaTeX (Rnw) exercise
   In case you prefer to keep on generating LaTeX tables with xtable() another route would be to change the markup of the R/exams exercise to Rnw (R/LaTeX). See the First steps tutorial on the R/exams web page for how to do that.

3. Markdown+Adaptive: Choose the right table markup depending on the output format
   Using the match_exams_call() function you can determine in a running exercise which exams2xyz() interface is being used to process it. So you could do

   type <- if(match_exams_call() %in% c("exams2pdf", "exams2nops")) "latex" else "html"
   print(xtable(tabla), type = type, ...)
   

   Then either LaTeX or HTML format is produced by xtable().

All three solutions work in principle but I think Solution 1 (kable()) is the best and most robust in your case.

Bonus remark: If you are using R/exams >= 2.4-0 you can use exams2moodle(...,table = TRUE) to get nicer table formatting in Moodle.

Answer 2

I use the following code snippet (with type = "latex"), when I require a PDF output:

```{r, eval=TRUE, only.contents=TRUE, echo=FALSE, results='asis', 
    warning=FALSE, message=FALSE, error=FALSE, comment=FALSE}
    library(exams)
    library(xtable)
    print(xtable(tabla), include.rownames=FALSE, type = "latex", comment=F)
```

And, when I require outputs for Moodle, I make use of the following code snippet (with type = "html"):

```{r, eval=TRUE, only.contents=TRUE, echo=FALSE, results='asis', 
    warning=FALSE, message=FALSE, error=FALSE, comment=FALSE}
    library(exams)
    library(xtable)
    print(xtable(tabla), include.rownames=FALSE, type = "html", 
    comment=F)
```

Results in PDF:

Results for Moodle: