pie charts in ggplot2

pie_plot.R

library(ggplot2)

data <- data.frame(
  months=c("jan", 'feb', 'mar', 'apr', 'may', 'june', 'july', 'august', 'sept', 'oct', 'nov', 'dec'),
  days=c(31,28,31,30,31,30,31,31,30,31,30,31),
  values=seq(12)
)

g.pie <- ggplot(data, aes(x='', y=days, fill=values)) +
  geom_col()+
  scale_fill_distiller(
    palette="RdBu",
    limits=c(
      -1*max(abs(values)),
      max(abs(values)))
    )+
  coord_polar(theta="y")
g.pie

ggsave('myplot.pdf', g.pie)