title: specify error bars with ggplot and facet_grid
body: <p>I have made a graph with <code>facet_grid</code> to visualize the percentage of litium in each group per treatment on each day.</p>
  
  <pre><code>library(ggplot2)
  library(Rmisc) 
  library(plyr)
  
  mus2 &lt;- summarySE(mus, measurevar="litium", 
                           groupvars=c("treatment", "group", "day"), na.rm = TRUE)
  
  mus2
  
  mus3 &lt;- mus2
  mus3$group &lt;- factor(mus3$group)
  
  ms.chl&lt;- ggplot(mus3, aes(x=group, y=litium, fill=treatment)) +
    geom_bar(stat="identity", colour="black") + facet_grid(~day) + theme_bw() 
  ms.chl
  </code></pre>
  
  <p>resulting with this:</p>
  
  <p><a href="https://i.stack.imgur.com/Jr2mW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Jr2mW.png" alt="enter image description here"></a></p>
  
  <p>For that I have two problems:</p>
  
  <p>I cant make proper error bars for the litium content PER GROUP. I have tried this, but I only get error bars per treatment.</p>
  
  <pre><code>ms.chl + geom_errorbar(aes(ymin=litium-se, ymax=litium+se), size=0.5,   
          width=.25,                    
          position=position_dodge(.9)) +
  facet_grid(~day)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/rvSAz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rvSAz.png" alt="enter image description here"></a></p>
  
  <p>I would like to have error bars from the total of each group</p>
  
  <p>and after that, my second question is: is it possible to represent the absolute value per group and the percentage only for each treatment?</p>
  
  <p>Data set (mus):</p>
  
  <pre><code>litium  group   treatment   day
  0.009439528 1   Control day1
  0.005115057 1   Control day1
  0.009742297 1   Control day1
  0.016515625 2   Control day1
  0.01074537  2   Control day1
  0.016300836 2   Control day1
  0.009538339 3   Control day1
  0.010609746 3   Control day1
  0.008928012 3   Control day1
  0.009425325 1   Control + bird  day1
  0.00561831  1   Control + bird  day1
  0.014622517 1   Control + bird  day1
  0.017702439 2   Control + bird  day1
  0.010545045 2   Control + bird  day1
  0.029109907 2   Control + bird  day1
  0.013737568 3   Control + bird  day1
  0.015174405 3   Control + bird  day1
  0.014583832 3   Control + bird  day1
  0.009244079 1   Control day2
  0.006591033 1   Control day2
  0.007592587 1   Control day2
  0.013676745 2   Control day2
  0.016208676 2   Control day2
  0.017593952 2   Control day2
  0.014003037 3   Control day2
  0.01163581  3   Control day2
  0.011643067 3   Control day2
  0.009229506 1   Control + bird  day2
  0.006423714 1   Control + bird  day2
  0.008653163 1   Control + bird  day2
  0.012441379 2   Control + bird  day2
  0.0204346   2   Control + bird  day2
  0.010017788 2   Control + bird  day2
  0.009745063 3   Control + bird  day2
  0.00967963  3   Control + bird  day2
  0.010291306 3   Control + bird  day2
  0.009466604 1   Fence   day2
  0.019611081 2   Fence   day2
  0.006796444 2   Fence   day2
  0.018928695 2   Fence   day2
  0.007787736 3   Fence   day2
  0.009409897 3   Fence   day2
  </code></pre>