title: Remove horizontal lines (ggplot2)
body: <p>I have asked nearly an identical question on here a few weeks back (<a href="https://stackoverflow.com/questions/9778959/eliminate-vertical-lines-ggplot">LINK</a>) and received a terrific response from <a href="http://wiki.stdout.org/rcookbook/" rel="nofollow noreferrer">Cookbook for R</a>.  It works beautifully.  The only problem is I don't really understand what's happening in the function.  Now I want to remove horizontal lines while still faceting and allowing <code>scales="free"</code> in the <code>facet_grid</code> function.  I can't figure out how to alter the response to make it work for horizontal lines.</p>
  
  <p>Here is some sample code to aid the discussion:</p>
  
  <pre><code>library(ggplot2)
  set.seed(10)
  CO3 &lt;- data.frame(id=1:nrow(CO2), CO2[, 2:3], 
             outcome=factor(sample(c('none', 'some', 'lots', 'tons'), 
             nrow(CO2), rep=T), levels=c('none', 'some', 'lots', 'tons')))
  CO3
  x &lt;- ggplot(CO3, aes(x=outcome)) + geom_bar(aes(x=outcome))+ 
       facet_grid(Treatment~Type, margins='Treatment', scales='free') 
  x +  theme_bw() + opts(axis.text.x=theme_text(angle= 45, vjust=1, hjust= 1))
  </code></pre>
  
  <p>I am, as always, very grateful for the help people give.  Thank you in advance.</p>