title: multi facet ggplot with secondary y axis?
body: <p>I have made multi facet <code>ggplot</code> using the <code>facet_wrap</code> function but could not find something that would let me create secondary y axis for a particular variable for all my plots.</p>
  
  <p>I have tried looking in google and found <a href="http://rpubs.com/kohske/dual_axis_in_ggplot2" rel="nofollow">http://rpubs.com/kohske/dual_axis_in_ggplot2</a> but i am not sure how to go from here to multi facet plots.</p>
  
  <p>I melted the dataset to get to get the different facet plots but cant figure how to put in a secondary y axis for the particular variable in group.</p>
  
  <pre><code>fig4bplot&lt;-    ggplot(fig4b,aes(x=as.Date(time),y=value,group=variable,color=variable))+geom_line(size=2,alph    a=4/5)+facet_wrap(~ Area)+theme_bw()
  fig4bplot&lt;-fig4bplot + theme(legend.position="bottom",legend.direction   ="vertical")+opts(axis.text.x = theme_text(angle = 90))
  fig4bplot&lt;-fig4bplot+xlab("Time")+ylab("One-Step Ahead Squared Forecast Error")+theme(text  = element_text(size = 30),
  axis.title =     element_text(size = 30),
  axis.text.x = element_text(size = 20,))
  </code></pre>