title: Error bars on stacked area graph with ggplot2
body: <p>I would like to add error bars on a stacked area graph created with <code>ggplot2</code>.</p>
  
  <p>My csv file looks like :</p>
  
  <pre><code>Day  Cat  Val   Error  
  0    A    0     0.00  
  0    B   44.77  1.16  
  0    C   54.64  0.88  
  13   A   1.34   0.32  
  13   B   22.78  0.45  
  13   C   38.33  2.12  
  19   A   1.95   0.35  
  19   B   24.00  2.25  
  19   C   40.30  3.86
  </code></pre>
  
  <p>I tried this :</p>
  
  <pre><code>ggplot(data=mydata, aes(x=Day,y=Val, group=Cat, fill=Cat,colour=Cat, ymax=Val + Error,   ymin= Val - Error)) +
   geom_area() +
   geom_errorbar(width=.5, color="black")
  </code></pre>
  
  <p>And I had this :</p>
  
  <p><img src="https://i.stack.imgur.com/bFqBT.png" alt="enter image description here"></p>
  
  <p>I'm happy with the area chart part of the graph but errors bars are not stacked on data points.</p>
  
  <p>I just getting started with <code>R</code> and I really don't know what the problem is.</p>
  
  <p>Besides, I've found this <a href="https://stackoverflow.com/questions/10417003/stacked-barplot-with-errorbars-using-ggplot2">tip</a> that use <code>geom_segment</code> to avoid overlapping between bars, but I failed to use it with this code.</p>
  
  <p>Thanks for helping me !</p>