title: ggplot2; how to draw group mean lines of two different groups in a categorical variable
body: <p>I have a following set of data;</p>
  
  <pre><code>    V1 V2  V3
   1: G1 P1 82.7
   2: G2 P1 64.6
   3: G2 P1 81.2
   4: G2 P1 95.3
   5: G1 P1 80.0
   6: G2 P1   NA
   7: G2 P1 65.0
   8: G1 P1 83.8
   9: G1 P1 88.0
  10: G1 P1 66.9
  11: G1 P1 56.8
  12: G1 P2 65.1
  13: G2 P2 57.7
  14: G2 P2 60.4
  15: G2 P2 18.6
  16: G1 P2 41.2
  17: G2 P2 47.0
  18: G2 P2 37.1
  19: G1 P2 18.8
  20: G1 P2 47.9
  21: G1 P2 40.0
  22: G1 P2 54.3
  </code></pre>
  
  <p>I made the following plot by using ggplot2;</p>
  
  <pre><code>ggplot(a,aes(x=V2,y=V3))+
      geom_jitter(aes(group=V1,color=V1,na.rm=T), position =position_jitterdodge())+
      stat_summary(fun.y="mean",geom="crossbar", 
               mapping=aes(ymin=..y.., ymax=..y..), width=1)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/u70Ex.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/u70Ex.png" alt="enter image description here"></a></p>
  
  <p>V1 contains two categorial variable, P1 and P2 and within them, there are two subcategories, G1 and G2.  What I like to do is to generate the plot with mean lines of G1 and G2 but the code above gives me the mean of categorical variables, P1 and P2.  </p>
  
  <p>I'd really appreciate any help on this. </p>
  
  <p>Thanks. </p>