title: Reducing legend size in ggplot beyond default size
body: <p>My goal is to make several plots with <code>ggplot</code> and combine them into a single plot using <code>grid.arrange</code> in the <code>gridExtra</code> package.</p>
  
  <p>I'm having an issue in that the legends in my <code>ggplot</code> (while appropriately sized for a single plot) are too large when I try to place the plots side by side with <code>grid.arrange</code>. The resulting combined plots reduce the x-axis but keep the legend original size. So the result is a very skinny plot, next to an needlessly large legend.  So I'd like to reduce the size of the legend in each plot, enough so that I can place my plots side by side. Or possible shrink them enough to bring them inside the actual plot without being to overbearing.</p>
  
  <pre><code>V1&lt;-rnorm(10)
  V2&lt;-rnorm(10)
  V3&lt;-rnorm(10)
  DF&lt;-data.frame(V1,V2,V3)
  
  
  ggplot(DF,aes(x=V1,y=V2,size=V3))+
  geom_point(fill='red',shape=21)+
  theme_bw()+
  scale_size(range=c(5,20))
  </code></pre>
  
  <p>This plot command produces a standard legend size to the right of the plot.</p>
  
  <p><img src="https://i.stack.imgur.com/HKK2M.jpg" alt="enter image description here"></p>
  
  <p>I've tried using different theme elements:</p>
  
  <pre><code>+theme(legend.key.size = unit(0.5, "cm")
  </code></pre>
  
  <p>or</p>
  
  <pre><code>+theme(legend.key.width=unit(0.3,"cm"),legend.key.height=unit(0.3,"cm"),legend.position = c(0.7, 0.8))
  </code></pre>
  
  <p>And while I can make the legend larger using these theme commands, I can't make the legend any smaller than the default legend. So is there any way to shrink the legend beyond the default size?</p>
  
  <p>I can also change the default size of my pdf device to make it wider and accommodate the large legends , but I'd like to work with a standard pdf size for now. </p>