Chapter 6 2번 문제

ggplot(data=mpg,aes(x=hwy,fill=drv))+geom_histogram(alpha=0.5)+labs(title="Histogram using facet_grid()",subtitle="Histogram of Highway Mile Per Gallon",color="drv",caption="Source: mpg",x="hwy",y="count")+theme_minimal()+facet_grid(rows=vars(drv))

## `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.