Updates in RTutor Main Branch

[skranz]

This issue shall describe updates I implemented in my RTutor branch. It is in particular targeted to maintainers of actively developed alternative branches (currently @MartinKies). Active discussion is encouraged.

[skranz]

The newest RTutor version contains a function make.hint.report (see f8e2dde and d4a4cf6) It creates an Rmd file from a problem set that shows for every chunk the sample solution, the given task code and the hint() message that would be shown if the task code would not have changed. This helps improving custom hints and to detect weaknesses in automatic hints. I plan to update RTutorSAGI at some point in the future in a similar fashion, so that the hints can be seen in the reports of common mistakes by students.

Based on the reports I updated again considerably the automatic hints (see 1d08d42). There are small changes like removals of typos in hint messages and larger changes. Importantly, when the user expression has some placeholder ___ in a function call, by default now a scrambled version of the whole function call we be shown. The previous hints() did not fit too well for tasks with placeholders.

[skranz]

Ok, as planned I now reworked the automatic hints again (see here 5e03dc0). For ggplot command chains and function calls with placeholders ___, by default the hint now attempts selective scrambling, i.e. it only scrambles the parts that differ in the student's solution from the sample solution. Only works if a single student solution can be matched as candidate. The code in hint.for.call does now look even less elegant, but the resulting hints look nicer, as far as I have tested.

[skranz]

Bugfix in the documentation. For some reason the Manuals link in the RTutor documentation https://skranz.github.io/RTutor/ did not work any longer. Perhaps due to changes in a newer pkgdown version. Corrected the corresponding code in https://github.com/skranz/RTutor/blob/master/_pkgdown.yml and now it works again.

[skranz]

There was a problem with the default svg device used in the shiny version of RTutor. Mac users who have not installed X-Quartz could not correctly show the problem set and got warning about missing Cairo libraries. I programmed a workaround in this commit. Since I don't have a Mac I could not really test it, but I hope it works.

[skranz]

There can appear a strange error in create.ps when called from an Rmd file and the RStudio Option Show output inline for all R Markdown documents is activated. I could not really solve the problem but now an error message is shown that shows how to circumvent the issue:

Note that there is a bug in the interaction of knitr and and RStudio in an RMarkdown document that shows output inline. There are two ways to fix to this proiblem:

1. Go in RStudio -> Tools -> Global Option -> R Markdown
   There turn off the option 'Show output inline for all R Markdown documents'
   
2. If you don't want to change those global options, put the code to create your RTutor problem set into a separate R file and run it there.