title: How can I remove the legend title in ggplot2?
body: <p>I have a question concerning the legend in ggplot2.</p>
  
  <p>Say I have a hypothetical dataset about mean carrot length for two different colours at two farms:</p>
  
  <pre><code>carrots&lt;-NULL
  carrots$Farm&lt;-rep(c("X","Y"),2)
  carrots$Type&lt;-rep(c("Orange","Purple"),each=2)
  carrots$MeanLength&lt;-c(10,6,4,2)
  carrots&lt;-data.frame(carrots)
  </code></pre>
  
  <p>I make a simple bar plot:</p>
  
  <pre><code>require(ggplot2)
  p&lt;-ggplot(carrots,aes(y=MeanLength,x=Farm,fill=Type)) + 
  geom_bar(position="dodge") +
  opts(legend.position="top")
  p
  </code></pre>
  
  <p>My question is: is there a way to remove the title ('Type') from the legend?</p>
  
  <p>Thanks!</p>