library(data.table)
library(dplyr)
library(ggplot2)
library(scales)

data <-
  mtcars %>%
  mutate(name = dimnames(mtcars)[[1]])


# bar chart with scale colour
data %>%
  ggplot(aes(x=reorder(name,mpg), y=mpg, fill=hp)) +
  geom_bar(stat='identity', width=0.8) +
  scale_fill_continuous(high='red', low='gray90') +
  scale_y_continuous(expand=c(0.01,0.01)) +
  coord_flip() +
  geom_text(
    aes(label=paste(mpg,'m/g')),
    size=3,
    hjust=1.2, vjust=0.2,
    fontface='bold') +
  theme(
    panel.background = element_blank(),
    axis.ticks = element_blank(),
    axis.title = element_blank(),
    axis.text.x = element_blank()) +
  labs(
    x='Miles Per Gallon',
    fill='Horse Power',
    title='MPG vs HP : Trade off')

fit <- lm(hp ~ poly(mpg,2), data=data)

data %>%
  ggplot(aes(x=mpg, y=hp)) +
  geom_point() +
  theme_bw() +
  theme(
    panel.grid = element_blank(),
    axis.title.x = element_text(angle=-10, face='bold'),
    axis.title.y = element_text(angle=20, face='bold')) +
  geom_line(
    aes(x=mpg, y=predict(fit, data.frame(mpg))),
    colour='red',
    linetype='dashed') +
  labs(title='MPG vs HP : Negative Relationship')