Plotting all variables from a data frame

plot_all_variables.R

library(ggplot2)
library(tidyverse)

df <- mtcars %>%
    gather(-mpg, key="var", value = "value")

ggplot(df, aes(x = value, y = mpg)) +
    geom_point(alpha = 0.3) +
    geom_smooth(method = "lm") +
    facet_wrap(~var, scales = "free") +
    scale_color_gradient(low = "orange", high = "blue") + 
    theme_bw()