title: Plotting bar plot below xyplot with same x-axis?
body: <p>I am trying to plot different types of plots (line plot and bar charts) beneath one another, they all have the same axis:</p>
  
  <pre><code>c1 &lt;- ggplot(data, aes(date, TotalMutObs)) + stat_smooth(se = FALSE) + 
              geom_point() + 
              opts(axis.title.x = theme_blank()) +
              ylab("Cumulative number of new mutations")   
  c2 &lt;- ggplot(data, aes(date, distance)) + stat_smooth(se = FALSE) + 
              geom_point() + 
              opts(axis.title.x = theme_blank()) + 
              ylab("Cumulative mean pairwise distance")   
  c3 &lt;- ggplot(data, aes(x = date, y = NbOfHorses)) + 
              geom_bar(stat = "identity") + 
              opts(axis.title.x = theme_blank()) + 
              ylab("Number of horses sampled")
  
  grid.arrange(c1, c2,c3)
  </code></pre>
  
  <p>However, the dates on the x-axis are not lining up for the different plots.<img src="https://i.stack.imgur.com/Qf5RX.png" alt="enter image description here"></p>
  
  <p>Here is some data to try it out:</p>
  
  <pre><code>date&lt;-c("2003-03-13","2003-03-25","2003-03-26","2003-03-27","2003-03-28","2003-03-31","2003-04-01","2003-04-02","2003-04-04","2003-04-08","2003-04-09","2003-04-10","2003-04-11","2003-04-14","2003-04-15","2003-04-17","2003-04-19","2003-04-21","2003-04-22","2003-04-28","2003-05-08");
  
  NbOfHorses&lt;-c("1","2","1","3","4","5","4","3","3","3","3","4","2","4","1","2","4","1","2","1","2");
  
  TotalMutObs&lt;-c("20","30","58","72","140","165","204","230","250","286","302","327","346","388","393","414","443","444","462","467","485");
  
  distance&lt;-c("0.000693202","0.00073544","0.000855432","0.000506876","0.000720193","0.000708047","0.000835468","0.000812401","0.000803149","0.000839117","0.000842048","0.000856393","0.000879973","0.000962382","0.000990666","0.001104861","0.001137515","0.001143838","0.00121874","0.001213737","0.001201379");
  
  data&lt;-as.data.frame(cbind(date,NbOfHorses,TotalMutObs,distance));
  </code></pre>
  
  <p>Cheers,
  Joseph</p>