title: ggplot2 manually adjust linetype of main plot but remove outline of geom_ribbon
body: <p>I have a problem in removing the outline of the confidence interval of geom_ribbon. Below is the code for a simplified version of the graph I would like to make: </p>
  
  <pre><code>Values &lt;- 1:20 + rnorm(20,20,sd=3);
  dat &lt;- data.frame(Group= rep(c("G1", "G2"), each=10),
      Xvals &lt;- 1:20,
      Yvals = Values,
      CIL = (Values -2),
      CIH = (Values +2))
  
  ad &lt;- ggplot(data=dat, aes(x=Xvals,y=Yvals,colour=Group)) +
  geom_line(aes(linetype=Group)) +
  scale_colour_manual(values=c("G1"="#FF6600","G2"="#0000FF")) +  
  scale_linetype_manual(values=c("G1"="solid", "G2"="dotdash" )) +
  geom_ribbon(aes(ymin=CIL,ymax=CIH,linetype=Group),alpha=0.1) 
  ad
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/vN3dv.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vN3dv.jpg" alt="enter image description here"></a></p>
  
  <p>I want to remove the outline of the confidence interval (just keep the shaded area)  but keep the manually adjusted color and linetype of the main lines (Yvals). Right now using geom_ribbon(aes(ymin=CIL,ymax=CIH,linetype=NA) - which would normally remove the outline - is not working since the linetype is already specified. Any help would be greatly appreciated. </p>