title: reversed legend using guide_legend()
body: <p>I am an absolute beginner in <code>ggplot2</code> and practicing to use <code>guide_legend()</code> functions. I am not quite sure why <code>guide_legend()</code> reverses the order of the legend. </p>
  
  <p>Here's the base example:</p>
  
  <pre><code>df &lt;- data.frame(x = 1, y = 1:3, z = 1:3)
  base &lt;- ggplot(df, aes(x, y)) + geom_raster(aes(fill = z))
  </code></pre>
  
  <p>This nicely produces a raster graph. </p>
  
  <p>However, when I add the following line, the order of legend gets reversed. Can someone please explain why this is happening?</p>
  
  <pre><code>base + scale_fill_continuous(guide = guide_legend())
  </code></pre>
  
  <p>I'd appreciate any thoughts. Is there anyway I can reverse the order?</p>
  
  <p>Thanks</p>
  
  <hr>
  
  <p><strong>Addition:</strong> I want to add that <code>reverse = FALSE</code> by default for guide_legend. I think <code>reverse=TRUE</code> will fix it, but I am not understanding the point of resetting the default value. Is there anything wrong that I am doing?</p>
  
  <p>Here's the guide: I am referring to <a href="http://docs.ggplot2.org/current/guide_legend.html" rel="nofollow noreferrer">http://docs.ggplot2.org/current/guide_legend.html</a></p>
  
  <p>Here's the pic: <a href="https://i.stack.imgur.com/hElR6.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hElR6.png" alt="enter image description here"></a> This pic is from above website.</p>