How to add a line in boxplot?

Question

I would like to add lines between "mean" in my boxplot.

My code:

library(ggplot2)
library(ggthemes)

Gp=factor(c(rep("G1",80),rep("G2",80)))
Fc=factor(c(rep(c(rep("FC1",40),rep("FC2",40)),2)))
Z <-factor(c(rep(c(rep("50",20),rep("100",20)),4)))
Y <- c(0.19 , 0.22 , 0.23 , 0.17 , 0.36 , 0.33 , 0.30 , 0.39 , 0.35 , 0.27 , 0.20 , 0.22 , 0.24 , 0.16 , 0.36 , 0.30 , 0.31 , 0.39 , 0.33 , 0.25 , 0.23 , 0.13 , 0.16 , 0.18 ,  0.20 , 0.16 , 0.15 , 0.09 , 0.18 , 0.21 , 0.20 , 0.14 , 0.17 , 0.18 , 0.22 , 0.16 , 0.14 , 0.11 , 0.18 , 0.21 , 0.30 , 0.36 , 0.40 , 0.42 , 0.26 , 0.23 , 0.25 , 0.30 ,  0.27 , 0.15 , 0.29 , 0.36 , 0.38 , 0.42 , 0.28 , 0.23 , 0.26 , 0.29 , 0.24 , 0.17 , 0.24 , 0.14 , 0.17 , 0.16 , 0.15 , 0.21 , 0.19 , 0.15 , 0.16 , 0.13 , 0.25 , 0.12 ,  0.15 , 0.15 , 0.14 , 0.21 , 0.20 , 0.13 , 0.14 , 0.12 , 0.29 , 0.29 , 0.29 , 0.24 , 0.21 , 0.23 , 0.25 , 0.33 , 0.30 , 0.27 , 0.31 , 0.27 , 0.28 , 0.25 , 0.22 , 0.23 , 0.23 , 0.33 , 0.29 , 0.28 , 0.12 , 0.28 , 0.22 , 0.19 , 0.22 , 0.14 , 0.15 , 0.15 , 0.21 , 0.25 , 0.11 , 0.27 , 0.22 , 0.17 , 0.21 , 0.15 , 0.16 , 0.15 , 0.20 , 0.24 ,  0.24 , 0.25 , 0.36 , 0.24 , 0.34 , 0.22 , 0.27 , 0.26 , 0.23 , 0.28 , 0.24 , 0.23 , 0.36 , 0.23 , 0.35 , 0.21 , 0.25 , 0.26 , 0.23 , 0.28 , 0.24 , 0.23 , 0.09 , 0.16 , 0.16 , 0.14 , 0.18 , 0.18 , 0.18 , 0.12 , 0.22 , 0.23 , 0.09 , 0.17 , 0.15 , 0.13 , 0.17 , 0.19 , 0.17 , 0.11)
X <- factor(c(rep(c(rep("B1",10),rep("B2",10)),8)))
DATA=data.frame(Y,X,Z,Fc,Gp)
p <- qplot(X, Y, data=DATA, geom="boxplot", fill=Z, na.rm = TRUE, 
                    outlier.size = NA, outlier.colour = NA)  +
          facet_grid(Gp ~ Fc)+ theme_light()+scale_colour_gdocs()+
          theme(legend.position="bottom") + 
          stat_summary(fun.y=mean, geom="point", shape=23, position = position_dodge(width = .75))

I have:

And the expected plot I want:

I tried this

p + stat_summary(fun.y=mean, geom="line", aes(group = factor(Z)))

and this

p + stat_summary(fun.y=mean, geom="line", aes(group = factor(X)))

but none of the above worked. Instead, I received the following error message:

geom_path: Each group consists of only one observation. Do you need to adjust the group aesthetic? geom_path: Each group consists of only one observation. Do you need to adjust the group aesthetic? geom_path: Each group consists of only one observation. Do you need to adjust the group aesthetic? geom_path: Each group consists of only one observation. Do you need to adjust the group aesthetic?

Thanks for your help !

Answer 1

This is not elegant but try this

tmp1 = aggregate(Y~., DATA[DATA$Z == 100,], mean)
tmp2 = aggregate(Y~., DATA[DATA$Z == 50,], mean)
tmp1$X2 = tmp2$X
tmp1$Y2 = tmp2$Y

graphics.off()
ggplot(DATA, aes(x = factor(X), y = Y, fill = Z)) +
    geom_boxplot(width = 0.5, outlier.shape = NA) +
    geom_segment(data = tmp1,
                 aes(x = as.numeric(factor(X)) - 0.125, y = Y,
                     xend = as.numeric(factor(X2)) + 0.125, yend = Y2)) +
    facet_grid(Gp ~ Fc)

Answer 2

Here's an alternative:

DATA$U <- paste(X, Z) # Extra interaction
qplot(U, Y, data = DATA, geom = "boxplot", fill = Z, na.rm = TRUE, 
      outlier.size = NA, outlier.colour = NA) +
  facet_grid(Gp ~ Fc) + theme_light() + scale_colour_gdocs() +
  theme(legend.position = "bottom") + 
  stat_summary(fun.y = mean, geom = "point", shape = 23, position = position_dodge(width = .75)) +
  stat_summary(fun.y = mean, geom = "line", aes(group = X)) + # Lines
  scale_x_discrete(labels = rep(levels(X), each = 2)) + xlab("X") # Some fixes