แกน x แบบหมวดหมู่

disease_counts <- who_disease %>%
	# Filter to on or later than 1999
	filter(___) %>% 
	mutate(disease = ifelse(disease %in% c('measles', 'mumps'), disease, 'other')) %>%
	group_by(disease, ___) %>%    # Add region column to grouping
	summarise(total_cases = sum(cases))

# Set aesthetics so disease is the stacking variable, region is the x-axis and counts are the y
ggplot(disease_counts, aes(___)) +
	# Add a column geometry with the proper position value.
	___(___)