Chapter 3

Workflow: Basics

Some important tips:

• Use Alt + - to write the assignment operator <- in R.

• In the comments, i.e, text written after # in code, explain the WHY of your code, not the WHAT or HOW.

3.5 Exercises

1. Why does this code not work?

   my_variable <- 10 
   my_varıable 
   #> Error in eval(expr, envir, enclos): object 'my_varıable' not found

   Look carefully! (This may seem like an exercise in pointlessness, but training your brain to notice even the tiniest difference will pay off when programming.)

   The code does not work because of the minor spelling difference, i.e., i vs. ī .

2. Tweak each of the following R commands so that they run correctly:

   libary(todyverse)  
   ggplot(dTA = mpg) +    
     geom_point(maping = aes(x = displ y = hwy)) +   
     geom_smooth(method = "lm)

   The corrected code is as follows:---

   library(tidyverse)  
   ggplot(data = mpg, mapping = aes(x = displ, y = hwy)) +    
     geom_point() +   
     geom_smooth(method = "lm")

3. Press Option + Shift + K / Alt + Shift + K. What happens? How can you get to the same place using the menus?

   The Alt + Shift + K shortcut brings up the Keyboard Shortcut Quick Reference. We could get to the same using menus as Help –> Keyboard Shortcuts Help.

4. Let’s revisit an exercise from the Section 2.6. Run the following lines of code. Which of the two plots is saved as mpg-plot.png? Why?

   my_bar_plot <- ggplot(mpg, aes(x = class)) +   
     geom_bar() 
   
   my_scatter_plot <- ggplot(mpg, aes(x = cty, y = hwy)) +
     geom_point() 
   
   ggsave(filename = "mpg-plot.png", plot = my_bar_plot)

   This time, the bar plot, i.e. my_bar_plot is saved into the file mpg-plot.png because in the arguments to the function ggsave() we have specified the name of the plot. The plot argument tells ggsave() the Plot to save, and by default, it goes to the last plot displayed.