Learning goals

• Visualizing numerical and categorical data and interpreting visualizations
• Recreating visualizations
• Getting more practice using with R, RStudio, Git, and GitHub

Getting started

⊕IMPORTANT: If there is no GitHub repo created for you for this lab, it means I didn’t have your GitHub username as of when I assigned the lab. Please let me know your GitHub username asap, and I can create your repo.

Go to the course GitHub organization and locate your assignment repo, which should be named lab-02-plastic-waste-YOUR_GITHUB_USERNAME. If you’re in the right place, it should similar to the following.

⊕NOTE: The GitHub screenshots in this lab are taken from another course with GitHub organization name “ids-s1-20” and instructor GitHub username “mine-cetinkaya-rundel”. Your screen should display our organization name “stat408-s22” in the repo path and your instructor’s GitHub username “staceyhancock” as the one who made the last commit.

Grab the URL of the repo, and clone it in RStudio. Refer to Lab 01 if you would like to see step-by-step instructions for cloning a repo into an RStudio project.

⊕NOTE: In Lab 01, you knitted to an .html file in order to see the compiled document. In this lab, we are knitting to a github_document (check out the YAML code at the beginning of your lab-02.Rmd file), which outputs a markdown file. Markdown is a “markup” language that lets you format text documents through a simple syntax. Unlike .html files, .md files are viewable from within Github!

First, open the R Markdown document lab-02.Rmd and click “Knit”. Make sure it compiles without errors. The output will be in the markdown (.md) file with the same name.

library(tidyverse)

plastic_waste <- read_csv("data/plastic-waste.csv")

Warm up

• Recall that RStudio is divided into four panes. Without looking, can you name them all and briefly describe their purpose?
• Verify that the dataset has loaded into the Environment. How many observations are in the dataset? Clicking on the dataset in the Environment will allow you to inspect it more carefully. Alternatively, you can type View(plastic_waste) into the Console to do this.

⊕Hint: If you’re not sure, run the command ?NA which will lead you to the documentation.

• Have a quick look at the data and notice that there are cells taking the value NA – what does this mean?

Exercises

Let’s start by taking a look at the distribution of plastic waste per capita in 2010.

ggplot(data = plastic_waste, 
       mapping = aes(x = plastic_waste_per_cap)) +
  geom_histogram(binwidth = 0.2)

One country stands out as an unusual observation at the top of the distribution. One way of identifying this country is to filter the data for countries where plastic waste per capita is greater than 3.5 kg/person.

plastic_waste %>%
  filter(plastic_waste_per_cap > 3.5)

## # A tibble: 1 × 10
##   code  entity     continent  year gdp_per_cap plastic_waste_p… mismanaged_plas…
##   <chr> <chr>      <chr>     <dbl>       <dbl>            <dbl>            <dbl>
## 1 TTO   Trinidad … North Am…  2010      31261.              3.6             0.19
## # … with 3 more variables: mismanaged_plastic_waste <dbl>, coastal_pop <dbl>,
## #   total_pop <dbl>

Did you expect this result? You might consider doing some research on Trinidad and Tobago to see why plastic waste per capita is so high there, or whether this is a data error.

⊕HINT: To facet by continent, use the code above that generated a histogram, but add facet_wrap(~continent).

1. Plot, using histograms, the distribution of plastic waste per capita faceted by continent. What can you say about how the continents compare to each other in terms of their plastic waste per capita?

⊕NOTE: From this point onwards the plots and the output of the code are not displayed in the lab instructions, but you can and should run the code and view the results yourself.

Another way of visualizing numerical data is using density plots.

ggplot(data = plastic_waste, 
       mapping = aes(x = plastic_waste_per_cap)) +
  geom_density()

And compare distributions across continents by coloring density curves by continent.

ggplot(data = plastic_waste, 
       mapping = aes(x = plastic_waste_per_cap, 
                     color = continent)) +
  geom_density()

The resulting plot may be a little difficult to read, so let’s also fill the curves in with colors as well.

ggplot(data = plastic_waste, 
       mapping = aes(x = plastic_waste_per_cap, 
                     color = continent, 
                     fill = continent)) +
  geom_density()

The overlapping colors make it difficult to tell what’s happening with the distributions in continents plotted first, and hence covered by continents plotted over them. We can change the transparency level of the fill color to help with this. The alpha argument takes values between 0 and 1: 0 is completely transparent and 1 is completely opaque. There is no way to tell what value will work best, so you just need to try a few.

ggplot(data = plastic_waste, 
       mapping = aes(x = plastic_waste_per_cap, 
                     color = continent, 
                     fill = continent)) +
  geom_density(alpha = 0.7)

This still doesn’t look great…

1. Recreate the density plots above using a different (lower) alpha level that works better for displaying the density curves for all continents.

2. Describe why we defined the color and fill of the curves by mapping aesthetics of the plot but we defined the alpha level as a characteristic of the plotting geom.

🧶 ✅ ⬆️ Now is a good time to knit your document and commit and push your changes to GitHub with an appropriate commit message. Make sure to commit and push all changed files so that your Git pane is cleared up afterwards.

And yet another way to visualize this relationship is using side-by-side box plots.

ggplot(data = plastic_waste, 
       mapping = aes(x = continent, 
                     y = plastic_waste_per_cap)) +
  geom_boxplot()

1. Convert your side-by-side box plots from the previous task to violin plots. What do the violin plots reveal that box plots do not? What features are apparent in the box plots but not in the violin plots?

⊕Remember: We use geom_point() to make scatterplots.

1. Visualize the relationship between plastic waste per capita and mismanaged plastic waste per capita using a scatterplot. Describe the relationship.

2. Color the points in the scatterplot by continent. Does there seem to be any clear distinctions between continents with respect to how plastic waste per capita and mismanaged plastic waste per capita are associated?

3. Visualize the relationship between plastic waste per capita and total population as well as plastic waste per capita and coastal population. You will need to make two separate plots. Do either of these pairs of variables appear to be more strongly linearly associated?

🧶 ✅ ⬆️ Now is another good time to knit your document and commit and push your changes to GitHub with an appropriate commit message. Make sure to commit and push all changed files so that your Git pane is cleared up afterwards.

Wrapping up

⊕Hint: The x-axis is a calculated variable. One country with plastic waste per capita over 3 kg/day has been filtered out. And the data are not only represented with points on the plot but also a smooth curve. The term “smooth” should help you pick which geom to use.

1. Recreate the following plot, and interpret what you see in context of the data.

🧶 ✅ ⬆️ Knit, commit, and push your changes to GitHub with an appropriate commit message. Make sure to commit and push all changed files so that your Git pane is cleared up afterwards and review the md document on GitHub to make sure you’re happy with the final state of your work.

Once you’re done, check to make sure your latest changes are on GitHub and that you have a green indicator for the automated check for your R Markdown document knitting.

Attribution

This lab is adapted from material in the Data Science in a Box course by Mine Çetinkaya-Rundel licensed under a Creative Commons Attribution Share Alike 4.0 International. Visit here for more information about the license.