Problem set 3

Data wrangling with {dplyr} and {tidyr}

Due by 23:59 on Saturday, September 26, 2026

Purpose

Chapter 3 and Chapter 4 in ModernDive introduce {dplyr}’s six core verbs for wrangling data: filter(), arrange(), select(), mutate(), group_by(), and summarise(), and {tidyr}’s two functions for reshaping data with pivot_longer() and pivot_wider().

In this problem set, you’ll practice using these functions on real data from the V-Dem (Varieties of Democracy) project. By the end, you should be able to:

  • Filter rows based on one or more conditions and arrange them by a column
  • Select a subset of columns to keep
  • Create new columns with mutate(), including recoding a numeric column into categories with ifelse()
  • Use group_by() and summarize() to calculate summary statistics (like averages) within groups
  • Chain {dplyr} verbs together with |>
  • Reshape data between wide and long formats with pivot_wider() and pivot_longer()
  • Feed wrangled data into ggplot() to make plots

Criteria for success

This problem is graded using a ✔+/✔/✔− system. I’m looking for correct wrangling logic and genuine attempts at the short written answers, not polished prose.

  • ✔+: All chunks run without errors and use the correct {dplyr} functions, columns, and logic. The datasets you create match the expected output shown in the instructions. The written answers correctly interpret the results (you don’t just restate numbers!), and the extension does something new and exciting rather than only copying a previous chunk.
  • ✔: This is the expected level of performance. All chunks run and produce mostly correct results; minor mismatches (e.g., column order, or rounding) are fine. Written answers are attempted and reasonable.
  • ✔−: Chunks are missing, don’t run, or use the wrong functions/columns for what was asked (e.g., using mutate() when summarize() was needed). Written answers are left blank.

You may work together in groups of up to four, but you must turn in your own answers and note who you worked with.

And remember: everything human-facing must be human-generated. Don’t submit AI-generated text. I want to hear your voice.

Also, if you do use LLMs to help with the code (I recommend not!), make sure you follow the guidelines from the syllabus about how to cite what you use.

How to submit

Submit a single rendered PDF on Canvas.

Instructions

  1. Download this .zip file. Make sure you unzip or extract it after you download it! Open the unzipped folder in Positron.

  2. Rename the Quarto file named your-name_problem-set-3.qmd to something that matches your name.

  3. Complete the tasks given in the Quarto file. You can definitely copy, paste, and adapt from other code in the document—don’t try to write everything from scratch!

  4. When you’re all done, render the document to Typst (pdf), PDF, or Word. Upload that file to Canvas. Do not upload a rendered HTML file (they don’t work on Canvas).