title: How to plot mean and standard error in Boxplot in R
body: <p>I have two categorical factors ('Habitat' and 'Locality'), and one continuous variable (T). 'Habitat' has two level and 'Locality' has eight levels. I want to change the default whiskers to represent the SE, and the median into the mean for each boxplot. Is there a way to do this and taking both of the categorical factors into account when plotting? Many thanks in advance. </p>
  
  <p>This is what I have done with the default setting of boxplot ggplot, showing the first and third quartiles with median intervals. </p>
  
  <pre><code>ggplot(data,aes(x=Locality,y=T)) + 
    geom_boxplot(aes(fill=interaction(Habitat,Locality), 
                     group=interaction(factor(Habitat),Locality)),
                 outlier.shape=1,outlier.size=3) + 
    theme_bw() + 
    theme(
      panel.grid.major=element_blank(),
      panel.grid.minor=element_blank(),
      axis.line=element_line(colour='black'),
      legend.position='none',
      axis.text.x=element_text(angle=90,hjust=1,size=12)) + 
    scale_y_continuous('T') + 
    xlab('Locality')
  </code></pre>