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R for Data Science: Annotations

Dec 4, 2023

From R for Data Science

1-Use geom_text() with infinite positions to place text at the four corners of the plot.


ggplot(mpg, aes(x = displ, y = hwy)) + 
  geom_point() + 
  geom_text(label = "top right", x = Inf, y = Inf, hjust = 1, vjust = 1) + 
  geom_text(label = "top left", x = -Inf, y = Inf, hjust = -0.1, vjust = 1) + 
  geom_text(label = "bottom left", x = -Inf, y = -Inf, vjust = -1, hjust = -0.1) + 
  geom_text(label = "bottom right", x = Inf, y = -Inf, vjust = -1, hjust = 1) 

ggsave("r-11-3-1-q1.png")

2-Use annotate() to add a point geom in the middle of your last plot without having to create a tibble. Customize the shape, size, or color of the point.


ggplot(mpg, aes(x = displ, y = hwy)) + 
  xlim(0,8) + 
  ylim(0,50) +
  geom_point() + 
  geom_text(label = "top right", x = Inf, y = Inf, hjust = 1, vjust = 1) + 
  geom_text(label = "top left", x = -Inf, y = Inf, hjust = -0.1, vjust = 1) + 
  geom_text(label = "bottom left", x = -Inf, y = -Inf, vjust = -1, hjust = -0.1) + 
  geom_text(label = "bottom right", x = Inf, y = -Inf, vjust = -1, hjust = 1) + 
  annotate(
     geom = "point",
     size = 5,
     x = 4,
     y = 25,
     color = "red") + 
    annotate(
     geom = "text",
     label = "center",
     size = 5,
     x = 4,
     y = 25,
     vjust = 1.2,
     color = "red") 
     
ggsave("r-11-3-1-q2.png")

3-How do labels with geom_text() interact with faceting? How can you add a label to a single facet? How can you put a different label in each facet? (Hint: Think about the dataset that is being passed to geom_text().)


ggplot(mpg, aes(x = displ, y = hwy)) + 
  geom_point() + 
  facet_wrap(~drv) + 
  geom_text(data = mpg |> filter(drv == "f"), x = 4, y = 40, label = "f", color = "blue", size = 10) +
    geom_text(data = mpg |> filter(drv == "4"), x = 4, y = 40, label = "4", color = "blue", size = 10)  + 
    geom_text(data = mpg |> filter(drv == "r"), x = 4, y = 40, label = "r", color = "blue", size = 10)  
    
ggsave("r-11-3-1-q3.png")

4-What arguments to geom_label() control the appearance of the background box?

  • label.padding - Amount of padding around label. Defaults to 0.25 lines.
  • label.r - Radius of rounded corners. Defaults to 0.15 lines.
  • label.size - Size of label border, in mm.
  • within mapping, colour, fontface, etc.
p <- ggplot(mtcars, aes(wt, mpg, label = rownames(mtcars)))

p + geom_label(mapping = aes(fill = factor(cyl)), colour = "white", fontface = "bold", 
  label.padding = unit(0.5, "lines"),
  label.r = unit(0.5, "lines"),
  label.size = 0.5)
  
ggsave("r-11-3-1-q4.png")

5-What are the four arguments to arrow()? How do they work? Create a series of plots that demonstrate the most important options.

  • angle changes the angle of the triangle point on the arrow
  • type changes whether the triangle is filled or not (open or closed)
  • length changes how big the arrow triangle is
  • ends changes the position of the arrow triangle, either on both ends, first, or last on the arrow segment

p <- ggplot(mpg, aes(x = displ, y = hwy)) + 
  geom_point()
  
  
p +  annotate(
          geom = "segment", 
          x = 3, y = 35, xend = 5, yend = 25, color = "blue",
          arrow = arrow(angle = 60, type = "closed", length = unit(0.5, "inches"), ends="first")
        )
        
ggsave("r-11-3-1-q5_1.png")

p +  annotate(
          geom = "segment", 
          x = 3, y = 35, xend = 5, yend = 25,color = "blue",
          arrow = arrow(angle = 10, type = "open", length = unit(1, "inches"), ends="last")
        )

ggsave("r-11-3-1-q5_2.png")