Module 04 Knowledge Check
5 questions. Pass mark 4 out of 5. Answer every question before checking the answer key below, then retry after reading the feedback.
1. A table with columns named Jan and Feb is untidy because…
- A. the names are abbreviated
- B. those are values of a variable, not variables
- C. the columns are numeric
- D. there are too few rows
2. Compared with nested calls, |> changes…
- A. the result
- B. the speed
- C. the reading order, from inside-out to top-to-bottom
- D. which packages are needed
3. Omitting .groups = 'drop' after a summarise() risks…
- A. an error on the next line
- B. the next verb operating within groups unnoticed
- C. losing the summarised columns
- D. the rows being reordered
4. In case_when(), putting >= 35 above >= 40 means…
- A. an error is raised
- B. values over 40 never reach the high band
- C. both conditions apply
- D. the .default is used instead
5. Before joining, anyDuplicated() on the key protects against…
- A. missing values in the key
- B. rows being multiplied by a repeated key
- C. the wrong join type
- D. column name collisions
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Answer Key and Explanations
Check these only after attempting every question.
1. B — those are values of a variable, not variables
Month cannot be filtered, grouped or joined while it lives in the header, and adding March means editing every piece of code.
2. C — the reading order, from inside-out to top-to-bottom
The pipe adds no capability. It puts the steps in the order they happen, which is most of what makes analysis code legible.
3. B — the next verb operating within groups unnoticed
The result stays grouped, so a following mutate() computes within each group. The numbers are wrong and nothing warns you.
4. B — values over 40 never reach the high band
It takes the first TRUE. The high band becomes unreachable, and the resulting column is entirely plausible and wrong.
5. B — rows being multiplied by a repeated key
If the right table has two rows for a key, every matching left row becomes two, and any sum afterwards is inflated.
Practical Check
Apply this module to your own work: complete the module activity for *Tidyverse Data Wrangling*, then write one sentence naming what your result shows and one naming what it does not.
Strong Answer Pattern
A strong answer names the task, the evidence used, the check performed, and the remaining limitation. It avoids "proved", "guaranteed", or "always" unless the evidence genuinely supports it.