Significant letters beneath geom_bars

Question

This is a bar plot of the iris dataset. The letters above each bar denote significant differences, obtained from a kruskal-wallis test. Although they are not too messy on this example plot, my real data has much larger error bars and differences in bar lengths. As such, the letters are all over the place and it becomes hard to read. I am wondering if it is possible to have the letters positioned beneath each bar, just above the x-axis. This way they would all align and be easy to read. What do ya reckon?

Code:

library(reshape2)
library(ggplot2)
library(agricolae)
library(Rmisc)

file<-iris

melt <- melt(file, id=c("Species"))

x1 <- summarySE(melt, measurevar = "value", groupvars = c("variable", "Species"), na.rm=TRUE)

d=list()
tmp=list()

for(i in 1:4){
  if(var(file[,i]) > 0){
    tmp<-c(tmp,colnames(file[i]))
    krusk <- kruskal(file[,i],file[,5],group=TRUE)
    krusk$groups<-krusk$groups[order(krusk$groups[,'trt']),]
    d[[i]]<-as.data.frame(krusk$groups)       
  }
} 

big_data=do.call(rbind,d)

plot<- ggplot(x1, aes(x = variable, y = value, fill = Species)) + 
  coord_flip()+
  geom_bar(stat = "identity", position =position_dodge(),colour="black",width=.7,size=.5)+ 
  geom_errorbar(aes(ymin=value-se, ymax=value+se), width=.1,size=.5,position=position_dodge(.7))+
  theme(
    axis.text = element_text(angle=0, vjust=1,size=8,face="bold"),legend.title=element_blank(),legend.position="bottom",
    legend.text=element_text(face="italic"))+
  labs(title=NULL,x=NULL,y=NULL)+
  geom_text(aes(label=big_data$M,colour=Species),position=position_dodge(width=1),vjust=.8,hjust=-1,size=3)

plot

Answer 1

Something like this:
For geom_text , set y = 0 , and hjust = 1.5 .
Note that the dodging widths for bars, error bars, and text are the same. Also note the the width of the bars is equal to the dodging widths, and thus the bars butt up against each other within each variable.

plot <- ggplot(x1, aes(x = variable, y = value, fill = Species)) + 
  coord_flip() +
  geom_bar(stat = "identity", position = position_dodge(width = .7),
     colour = "black", width = .7, size = .5) + 
  geom_errorbar(aes(ymin = value-se, ymax = value+se), position=position_dodge(width = .7),
     width = .1, size = .5) +
  geom_text(aes(y = 0, label = big_data$M, colour = Species), 
     position=position_dodge(width = .7), hjust = 1.5, size = 3) +
  theme(
    axis.text = element_text(angle=0, vjust=1,size=8,face="bold"),legend.title=element_blank(),legend.position="bottom",
    legend.text=element_text(face="italic")) +
  labs(title=NULL,x=NULL,y=NULL)

plot