title: How to change legend of facet_grid?
body: <p>I used R and ggplot to do a small-multiple graph.</p>
  
  <pre><code>ggplot(data=datatest,aes(x=Percentage,y=Accuracy,group=interaction(Classifiers, Feature), color=interaction(Classifiers, Feature)))+geom_line()+facet_grid(OS ~ Dataset)
  </code></pre>
  
  <p>The graph I got is:
  <a href="https://i.stack.imgur.com/fJB5B.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fJB5B.jpg" alt="enter image description here"></a></p>
  
  <p>How can I remove change the legend, for example, I want to change interaction(Classifiers,Feature) to just 'Approaches', and also, how to change like SVM.Ngram, LG.WE, SVM.WE to just 'approach1','approach2', and 'approach3'.</p>