Если я правильно понимаю, это то, что вы хотите.
library(ggplot2)
library(tidyverse)
# add column name on the car names
mtcars <- mutate(mtcars, car_name = row.names(mtcars))
# factor to make car in order by mpg
mtcars$car_name <- factor(mtcars$car_name, levels = mtcars$car_name[order(-mtcars$mpg)])
# plot by car and mpg
by_car <- ggplot(mtcars, aes(car_name, mpg, fill = car_name)) + geom_bar(stat = "identity")+ xlab('Car Name') + ylab('Miles Per Gallon') +
ggtitle('Distribution of Cars by Mileage') + theme(axis.text.x = element_text(angle = 90, hjust = 1))