Central error bars (geom_errorbar) horizontally on bars (geom_bar)

Question

How would I place error bars in the center of the corresponding color bars?

df1 <- data.frame( supp = c("OJ","OJ","OJ","VC","VC","VC"), dose = c(0.5,1,2,0.5,1,2), len = c(13.23,22.7,26.06,7.98,16.77,26.14), se = c(1.41,1.27,0.84,0.87,0.8,1.52) ) df1$dose <- factor(df1$dose) ggplot(df1, aes(x=dose, y=len, fill=supp)) + geom_bar(stat="identity", position=position_dodge()) + scale_fill_manual(name = "", values = c("deepskyblue1", "green")) + geom_errorbar(data = df1[1:3,], aes(ymin=len-se, ymax=len+se), width=.4, colour=c("deepskyblue1"), position=position_dodge(.9)) + geom_errorbar(data = df1[4:6,], aes(ymin=len-se, ymax=len+se), width=.4, colour=c("green"), position=position_dodge(.9)) 

Answer 1

Since the data for the error bars is in the same data frame, where the data for the bars you do not need to provide the argument data= in geom_errorbar() , and there is also no need to call geom_errorbar() twice.

You must specify the geom_errorbar() ymax and ymax in aes() , also color=supp in aes() will ensure that the error bars are colored according to the supp values. To get the same colors as for the bars, add scale_color_manual() with the same color names. With the argument position=position_dodge(0.9) you can get errorbars in the center of the bars.

 ggplot(df1, aes(x=dose, y=len, fill=supp)) + geom_bar(stat="identity", position=position_dodge()) + scale_fill_manual(name = "", values = c("deepskyblue1", "green")) + geom_errorbar(aes(ymin=len-se, ymax=len+se,color=supp), width=.4, position=position_dodge(.9))+ scale_color_manual(name = "", values = c("deepskyblue1", "green"))