19 Modifying the axes

Tip

flowchart LR
  ADA(Axis)
  ADA -->ADAA(lim):::api
  ADA -->ADAB(lab):::api
  ADA -->ADAC(coord_flip)
  ADA -->ADAD(scale)

  classDef api fill:#f96,color:#fff

library(tidyverse)

Here let us focus on two families of useful helpers that let you make the most common modifications. xlab() and ylab() modify the \(x\)- and \(y\)-axis labels:

ggplot(mpg, aes(x = cty, y = hwy)) +
  geom_point(alpha = 1 / 3)

ggplot(mpg, aes(x = cty, y = hwy)) +
  geom_point(alpha = 1 / 3) + 
  xlab("city driving (mpg)") + 
  ylab("highway driving (mpg)")

# Remove the axis labels with NULL
ggplot(mpg, aes(x = cty, y = hwy)) +
  geom_point(alpha = 1 / 3) + 
  xlab(NULL) + 
  ylab(NULL)

xlim() and ylim() modify the limits of axes:

ggplot(mpg, aes(x = drv, y = hwy)) +
  geom_boxplot()

ggplot(mpg, aes(x = drv, y = hwy)) +
  geom_boxplot() + 
  xlim("f", "r") + 
  ylim(20, 30)

# Use NA for the lower limit in ylim() to automatically calculate
# it based on the minimum value in the data,
# while setting the upper limit to 30.
ggplot(mpg, aes(x = drv, y = hwy)) +
  geom_boxplot() + 
  ylim(NA, 30)

Changing the axis limits in ggplot2 converts values outside the specified range to NA. To suppress warnings associated with these NA values, you can use na.rm = TRUE. However, exercise caution: this conversion to NA occurs before the computation of summary statistics like the sample mean. As a result, it may affect the accuracy of these statistics, leading to potentially misleading interpretations.

# This plot ylim to restrict the y-axis from 20 to 30, 
# suppressing NA-related warnings with na.rm = TRUE.
ggplot(mpg, aes(x = drv, y = hwy)) +
  geom_boxplot(na.rm = TRUE) + 
  ylim(20, 30)

Exercise F

Change the \(x\) lable and \(y\) label for the scatterplot of cty and displ using appropriate texts.

First render a frequency plot demonstrating the counts of cars grouped by manufacturer in the mpg data. Then, set the \(x\)-axis limit so that the chart only displays the counts for “audi”, “mercury” and “volkswagen”.