dots and error bars

library(ggplot2)
library(dplyr)
data(mtcars)
sem <- function(x) sd(x)/sqrt(length(x)) #std error

mtcarsx <- mtcars %>% group_by(cyl) %>% summarize(meanx = mean(wt), semx = sem(wt)) %>% mutate(upr = meanx + semx, lwr = meanx - semx)
mtcarsx

ggplot(mtcarsx, aes(x=factor(cyl), y=meanx))+
  geom_errorbar(aes(ymin=lwr, ymax=upr), width=.4)+
  geom_line() + 
  geom_point() +
  geom_point(data=mtcars, aes(factor(cyl), wt), size=3, color='gray77') + 
  theme_bw()