How to add answer specific feedback to dist3.Rmd? - r

Question

I'm looking at the dist3.Rmd example template from here: http://www.R-exams.org/templates/dist3/. The solution markdown is the general feedback provided after submission. I want to create feedback.
Solution
========
The distance $d$ of $p$ and $q$ is given by
$d^2 = (p_1 - q_1)^2 + (p_2 - q_2)^2$ (Pythagorean formula).
Hence $d = \sqrt{(p_1 - q_1)^2 + (p_2 - q_2)^2} =
\sqrt{(`r p[1]` - `r q[1]`)^2 + (`r p[2]` - `r q[2]`)^2}
= `r round(sol, digits = 3)`$.
\
```{r distplot, echo = FALSE, results = "hide", fig.path = "", fig.cap = ""}
par(mar = c(4, 4, 1, 1))
plot(0, type = "n", xlim = c(0, 6), ylim = c(0, 6), xlab = "x", ylab = "y")
grid(col = "slategray")
points(rbind(p, q), pch = 19)
text(rbind(p, q), c("p", "q"), pos = c(2, 4))
lines(rbind(p, q))
lines(c(p[1], p[1], q[1]), c(p[2], q[2], q[2]), lty = 2)
```
If the answer choice is correct, I'd like the general feedback to popup and if the answer is wrong, I'd like for the pythagorean formula and the image prompt to show up but not the calculation. How can I accomplish this?

Answer 1

Given your jargon about "general feedback" I assume this is related to Moodle and the exams2moodle() interface in R/exams.
I tried to find out whether the feature you describe can be specified using Moodle XML format but was not successful. So at the moment this is certainly not possible in R/exams and I'm not sure whether it would be possible in Moodle XML. If anyone is aware of a solution in Moodle XML, I would be interested and could check whether it would be possible to add this to exams2moodle().
Update: Following the discussion in the comments with #ArvindMurali I briefly discuss here how it is possible to include images in the specific feedback from the "solution list". However, I still don't see how to separate specific and general feedback between different iterations of answering the question.
If you make a copy of dist3.Rmd to, say, dist4.Rmd you just need to modify two lines. In the options for the r distplot code chunk in line 35, add fig.show = "hide". And in the r solutionlist chunk in line 46 replace the answerlist(...) command with:
answerlist(ifelse(sc$solutions,
"This is correct!",
"This is not correct, please consider: <br/> ![](distplot-1.png)"),
markup = "markdown")
For preparing this for Moodle you then need to use pluginfile = FALSE so that the image is really embedded directly into the specific feedback (rather than via Moodle's plugin file declaration).
set.seed(1)
exams2moodle("dist4.Rmd", pluginfile = FALSE)
Then, the specific feedback for each incorrect item will display the plot from the r distplot chunk.
The formatting is not great but it works - so far so good.
The problem is that in addition to this specific feedback, the general feedback will also be displayed at the end - always, as far as I can see. If there were a way to delay this in Moodle, then I could check whether it is possible to interface this in R/exams.