How to change the correct answer of a question and replicate exams from scratch when exshuffle is on (package 'exams')?

Question

I have the following question, where the argument of exsolution is {0010} but it should be {1000}

egin{question}
What is the capital of Italy

egin{answerlist}
  item Rome
  item Paris
  item Vienna
  item Madrid
end{answerlist}
end{question}
extype{schoice}
exsolution{0010}
exshuffle{4}

I have corrected the error and re-run the processes of creating and grading exams from scratch using the same seed. Unfortunately, the sequence of answers in this question changes (note exshuffle{4}), so the grades assigned to this particular question are wrong. All other questions are OK.

question from:https://stackoverflow.com/questions/65897770/how-to-change-the-correct-answer-of-a-question-and-replicate-exams-from-scratch

Answer 1

Due to the way that exshuffle is implemented it is not easy to just change the {answerlist} and/or exsolution and get the right resulting exam.

Instead I would recommend to go through the meta-information and fix it there. I presume that you are generating the exams with exams2nops() and have stored the RDS with the metainformation, right? I will produce such a file via:

set.seed(1)
exams2nops(c("capitals.Rnw", "italy.Rnw", "switzerland.Rnw"), n = 5, dir = ".")

Thus, there are five exams with 3 exercises each with your problematic exercise italy.Rnw in second place. The metainformation is stored in metainfo.rds which we can read again via

x <- readRDS("metainfo.rds")

Now x is a list of 5 elements (exams), each of which has 3 elements (exercises), which have elements question, questionlist, solution, solutionlist, metainfo, and supplements. Here, we need to inspect the questionlist in order to fix the metainfo$solution. Currently, Vienna is marked as being correct:

x[[1]][[2]]$questionlist
## [1] "Madrid" "Vienna" "Rome"   "Paris" 
x[[1]][[2]]$metainfo$solution
## [1] FALSE  TRUE FALSE FALSE

However, it should be Rome:

x[[1]][[2]]$questionlist == "Rome"
## [1] FALSE FALSE  TRUE FALSE

So we can loop through this and save the result. Just to be safe, we also store the original RDS file:

x <- readRDS("metainfo.rds")
file.copy("metainfo.rds", "metainfo-orig.rds")
for(i in seq_along(x)) {
  x[[i]][[2]]$metainfo$solution <- x[[i]][[2]]$questionlist == "Rome"
}
saveRDS(x, "metainfo.rds")

Final remark: There is also an element metainfo$string that is used when extracting exams_metainfo(). If we wanted to use that, we would need to fix the $string as well. But for nops_eval() it is sufficient to fix the $solution.