ggplot2:: Facetting plot with the same reference plot in all panels
问题 I would like to facet a plot, but with a reference plot in each panel. Let me try to show with pictures what I want to achieve: My example data_frame: require(dplyr) df <- data_frame( id = c(rep('ctr',40), rep('pat',80)), class = c(rep('ctr',40), rep(c('a','b'), each = 40)), rank = rep (1:20,6), mean = c(rep(seq(3,-3, length.out = 20),2), rep(seq(1,-4, length.out = 20),2), rep(seq(-2,-8, length.out = 20),2)), sd = rep(seq(1.2,0.8, length.out = 20), times = 6), exam = rep(c('blue','red'), each