title: Add horizontal error bar to single point in ggplot
body: <p>I have plotted 2 normal curves in <code>ggplot2</code>, and I've added a separate point at the maximum of the first curve. I want to add an error bar to this point which has width 1. Here is my code:</p>
  
  <pre><code>library(ggplot2)
  library(reshape2)
  x=seq(from=0,to=5, length=100)
  y=dnorm(x,2,0.5)
  z=dnorm(x,3,1)
  sf=data.frame(d=2,e=0.8, se=0.5)
  normalplot=data.frame(x,y,z)
  colnames(normalplot)=c("index", "Type 1", "Type 2")
  k=melt(normalplot, id="index")
  colnames(k)=c("index", "Method", "value")
  
  ggplot(k, aes(x=index, y=value, colour=Method))+
    theme(axis.text.y=element_blank(), axis.ticks.y=element_blank())+xlab("")+ylab("")+
    geom_line()+
    geom_point(data=sf,aes(d,e),colour="red",size=2)+
    geom_errorbarh(sf,aes(xmax =d+se, xmin =d-se))
  </code></pre>
  
  <p>This does not work, but I cannot see why. I also want to add another point at the maximum of the second normal curve at (3,0.4) also with an error bar. Any help?</p>