Draw "error bars" for multiple categories

Question

I have a data frame with (min,max) values for different categories, for example:

    case1     case2
 1 0.8945 0.8943867
 2 0.8950 0.8952849

I would like to make a plot where, for each category, only a vertical segment with short horizontal segments at the bottom and at the top is drawn: it looks like an error bar, but it doesn't have a central point. If necessary, I can live with the central point, though. Each segment must be labeled with the corresponding category name, as the boxes of a boxplot:

boxplot(df,cex.axis=1.5)

But the look of the bars must be that of functions such as plotCI, segments, etc.:

require(plotrix)
x=0:1
plotCI(x,apply(df,2,mean),li=df[1,],ui=df[2,],xlab="categories",ylab="values")

This looks fine, but the x-axis is numerical, while I need category names on the x-axis. Also, I don't like the bars to be so far away from each other, and so close to the plot margins. Is it possible to put them closer to the center, as for the boxes of a boxplot?

Answer 1

You have at least two possibilities:

• Without ggplot2:

  require(plotrix)
  plotCI(apply(df,2,mean),li=df[1,],ui=df[2,],xlab="categories",ylab="values")
  axis(side = 1, at = c(1,2), labels = c("case1", "case2"))
  

• With ggplot2:

First redefine your data.frame:

df2 = data.frame(vmin =  c(0.8945, 0.8943867), vmax=c(0.8950, 0.8952849), case=c("case1", "case2"))

Then, use geom_errorbar

library(ggplot2)
p <- ggplot(df2, aes(ymin = vmin, ymax = vmax, x = case))
p + geom_errorbar()