```r
data("mussels")
d<-mussels
g0 <- ggplot(d,aes(x=Site,y=Lshell))
g_mean<-g0+stat_summary(fun=base::mean,geom="point")
g_mean
```

<img src="qs_21_files/figure-html/unnamed-chunk-72-1.png" width="672" />