แผนภูมิแท่งแบบซ้อนเบื้องต้น

disease_counts <- who_disease %>%
	mutate(disease = ifelse(disease %in% c('measles', 'mumps'), disease, 'other')) %>%
	group_by(disease, year) %>% # note the addition of year to the grouping.
	summarise(total_cases = sum(cases))

# add the mapping of year to the x axis. 
ggplot(disease_counts, aes(___, y = total_cases, fill = disease)) +
	# Change the position argument to make bars full height
	geom_col(___)